As many commenters rightly found out, these devices are regenerative receivers. If you are interested in "real" radar sensors, I propose watching video #439
Today my RCWL-0516 's arrived from ali-express, could'nt wait to do some experiments .. (did'nt add any additional components) Wow .. these things are unbelievable sensitive especially moving to or away from them. Over the entire distance of my buro (~4 Meter) a movement of 2 cm's of my hand is enough to trigger it. Thanks a lot Andreas for making this great video!
They are really too sensitive. I tried connecting one(rcwl-0516) to a nodered counter node via a 8266 microcontroller to detect the number of detections and found that even with nobody present in the apartment it is still detecting movement at times.I live in an apartment building so I assume it is detecting movement through the walls in the other apartments.I did not try to reduce the sensitivity yet. Has anybody tried it with resistors to reduce sensitivity?
I have been using RCWL-0516 Microwave Radar Sensors in a smart lighting application (integrated with ESP32 developer boards) for several months now. To this video I would add a couple notes. The first is that though the sensors do not interfere with each other, they can get false triggered from the ESP32. This effect falls off after a centimeter or two. Lesson learned, be careful mounting the sensors to the same circuit board as your controller. The lack of directionality and ability to penetrate wood is amazing and perfect for my application. The sensors often detect me just before I enter the rooms with my lights. My sensors appear to work through regular glass. I mounted some of my smart lights on my double pane window and the detectors see me from outside my house. My different experience may be explained by the sensors penetrating the wood but it may be that I’m using traditional glass and your video reported testing against acrylic glass. The later makes sense as acrylic would act more like water than silicate. A final note on voltages... Though it does take 5V to power the sensors, the sensor output voltage is 3.2-3.4V. This is perfect if you’re powering your circuit with a 5V supply and reading the signal with a CMOS device like the ESP32.
Thank you so much for doing this, prior to this video I was not aware of these cheap radar sensors (the rcwl-0516 is on eBay for about a dollar). As usual your testing was detailed and your explanation was perfect. Another excellent video!
I keep repeating myself... great video ! A very good comparison which is very usefull. It will defenately help me for choosing the right one. Thanks Andreas !
Thanks for checking out these various sensors. I think I will find them very useful and it is great to be able to rely on you to sort the features of the many choices available!
Hi. I've recently discovered the RCWL-0516 and in search of more specifics I've then found your video.Your extensive tests are very helpful. Especially the needed voltage to run it, the diagnosis if the devices interfere with each other, the directionality and what they penetrate. Viele Grüsse aus dem Hackerspace Ruum42 aus der Ostschweiz.
I discovered those modules recently, and still waiting for them to arrive. You saved me a lot of time, i don't have to make a comparative test. Thank you
First of all, great video! These motion detection radars most likely works in doppler mode, which is sensitive to frequency close to its emitting frequency, which explains why 2 of the same model do not interfere with each other, and why they don't detect stationary object.
Perfect timing! I just received four RCWL-0516 units. I could not decide which variety to get and it appears randomness intervened to select a good choice for me. These evaluations of similar products are both interesting and useful. Thank you!
Very good, thank you. You have to bare in mind that a lot of double glazing windows have an aluminium coating all over the glass for thermal insulation/reflection, and so this will no doubt explain away a lot of the RF attenuation you found when doing the double glazing window through tests.
IRC these units don't work like a radar. IRC they don't receive a signal back from what they send out. They just emit a continuous wave and monitor how much power it is using to transmit. if something moves in it's "field" it changes the SWR standing wave ratio of the transmitter, causing it to us more or less power that the comparitor uses to cause a trip.
Depending of the distance between the transmitter and the reflections the signal arrives at the receiver either in phase, out of phase or in betwee at the receiver. The two signals are present on the transistor at the same time. As the transistor is a nonlinear device the two signals mix together and generate a DC offset dependant of their relative phase. When an object is moving in front of the sensor this DC offset oscillates at a very low frequency. This signal is amplified and detected by a chip which is very similar to the BISS0001 used in PIR sensors as the output signals of these sensors are nearly identical. The only difference is that this chip includes a built in 3.3v regulator.
@@keesterwee4890 They do not work the same way as the shop theft systems. They rely on the same technology used with prox or access control tags. The arches transmit an rf signal that sweeps a small bandwidth at around the 3.8ghz mark. The tags on the shop item have an antenna tuned to that frequency, a small capacitor and transistor in a smc package connect to the antenna. The RF energy from the arches powers the IC in the alarm tag and creates a simple oscillation resulting in a reflection of RF power at a slightly offset frequency or delay depending on the system type. The signal return to the arch triggers the alarm. It's just come over to the uk but stores in Japan have been using this for years with IC's that will return a pulsed code instead of just a "present" signal as with the theft alarms. These shops in Japan allow you to swipe your customer card and then go round the store filling your trolly. When you exit the store all the prox codes are read and you are billed for the goods. Sadly until all the packaging manufacturers and the industry incorporate smart IC technology we cannot switch to this system. I tested a product with a smart tag a while back and was not surprised to discover that the coded return from the product matched the bar code ! I assume this has been done to make life easier for any stores that have a barcode database. They only then need switch from a barcode reader to an RF based one. I can't see unmanned stores taking of in the UK just the stock itself ;-) With regards to how these little detectors do operate see my reply to "Sirus"
Excellent details. Thank you. It will be great if you can make a video on using those as metal detectors! Like detecting metal hidden underground or maybe behind a large lump of sand. Those treasure hunters will love the video :)
The long awaited radar sensor comparision you promised to do! You have not forgotten it! Now I know these devices work and which one to buy. Thank you so much!
Andreas, The working principle of these type of radars (radio detection and ranging) is well understood and used in many applications already for many years. In a nutshell: These radars typically work in the L to X band : 1GHz-12.5GHz They are frequency modulated continuous waves radars typically with linear frequency sweeps, say 100Mhz Example: a saw tooth frequency of 100kHz changes the frequency linearly from 2.4GHz to 2.5GHz in 10 microseconds The transmitted signal is sent into the world via the antenna The received signal that bounced back from an object on a distance d from the antenna is received back with a delay of 2d/c seconds (c speed of light 3*10E8m/sec). Example: if d is 3m, the delay is 20 nanoseconds. During this delay the frequency of the transmitter has increased 200kHz versus the received signal. (100MHz*20nsec/10usec) The transmitted and received signal are combined (mixed) and passed through a highly nonlinear element, i.e a diode. The output of this process are waveforms that include the sum and difference of the 2 signals and their harmonics Through proper filtering we can isolate the frequency difference (200kHz), calculate the delay (20 nsec) and the related object distance (3m) Kind regards
Thanks for your explanations. I only doubt if or how all these functions can be done with only one active component. That is the miracle for me... If you look at a newer video we use the principles you mentioned for a bicycle counter. But this device will have much more parts.
Dude - did you copy that out of a textbook? Nice explanation for doppler ranging radar. But that's not what this does. It just detects motion by mixing the transmitted and received signals together and detects a low-frequency beat. No ranging info. No speed info. Just detects motion.
Good video. I like how you compared these units and gave a clear overview of their main advantages. (Good to see I picked the right one when randomly ordering the cheapest radar-sensor I could find). Thanks!
This one is the original of the cheaper LiDARs on the market but currently sold out: www.3dxr.co.uk/product/benewake-tfmini America: www.seeedstudio.com/Seeedstudio-Grove-TF-Mini-LiDAR-p-2996.html America 2: www.robotshop.com/en/benewake-tfmini-micro-lidar-module-12-m.html This one is a China knockoff but perhaps the same: www.aliexpress.com/item/RCmall-Lidar-Range-Finder-Sensor-Single-Point-Micro-Module-for-Arduino-Pixhawk-Cable-Benewake-TFmini-Drone/32852024277.html High Quality LiDAR for reference (older) : www.robotshop.com/en/lidar-lite-3-laser-rangefinder.html
Thanks for this comprehensive and systematic comparision. It comes very handy to me because I also received a sensor similar to XYC-WB-D1 for playing around and looking for a helpful application. Unfortunately (?) most helpful application are already covered in my environment. It is really an excellent work to do all that with just one (1) transistor and some passives. Chapeau!
Are Jayem He's speaking to a specialized group with this subject matter. He is very good at what he does, but there are not many who have an interest in sensors.
Besides the particular topic (sensors) - which is gaining traction with many makers and electronics diy hobbyists - I find a good number of our host's presentations balanced, informative and accessible, and creatively interesting. By doing this, what would be specialized subject is delivered for a wider audience to ponder and spark ideas.
I bought a sensor which is marked "2.7GHz" from Aliexpress and was quite surprised by the spectrum of signal which it emits. It is not a narrow "spike" but rather wide, maybe 1 MHz wide. Is that happening because of poor Q of PCB resonator?
1 MHz isn't that bad for these type of devices. with an arduino your frequency can vary as much as 0.5% - at 3 GHz that would be 1.5 MHz just from inaccuracy.
Thanks for taking the time to run through these. Wish I had found this video before I bought 5 of each of the RCWL and HFS boards. I need 3 working units (always buy extra from China). Looks like the cheaper boards will be the best fit. NBD. At the prices these things are going for these days I can throw the others in a drawer to use for something else some day. The HFS boards will be better if I need something to be directional.
Are you sure the RCWL-0516 does not work on 3.3V? I really cannot see a reason why it shouldn't work if you power it with 3.3V on the 3.3V pin. Usually a voltage regulator doesn't care much if you power its output with the right voltage and no input connected... Even if the voltage regulator is integrated within the IC. And I don't think the unregulated input voltage is used anywhere else except on the voltage regulator input. You should try it.
Movement is almost never detected by the red shift (frequency change) of the reflected radio wave. Speed is measured in a totally different way, with a so-called doppler radar. Doppler radar measures the distance of an object by measuring the time elapsed between sending out and receiving the same signal. It sends out two singals, and measure the change of distance between those two signals.
I think there is a misunderstanding here? The RADAR I was working on cost just under £2,000,000 and use multiple pings etc. However, I understand these very low-cost units operate exactly as described in the video. I purchased mine for
Hello Andreas, Before I begin, I like your videos a lot. In your video at 15:04 min. you explain that the RCWL-0516 cannot work in a 3.3 volt environment, I make a mistake and put 3.3 volt as input voltage. So 3.3 volt on the 3.3 pin and GND on the GND pin then a diode connected on the Out pin and GND, and wonder the RCWL-0516 works also, it detects movements like before. I think that you can use the module from 3.3 volts and if you have 4 volts till 28 volts you must connect the input voltage on the VIN pin. www.elecrow.com/rcwl-0516-microwave-radar-sensor-switch-module-body-induction-module-4-28v-100ma.html Greetings from Holland, Jan-Henk van Kesteren
Thanks for your link. Maybe there are different versions of the same modules around, as in many other cases. Or I did something wrong, which also happens from time to time.
Great video Andreas! I found this GitHub repo that has a schematic of the RCWL-0516 : github.com/jdesbonnet/RCWL-0516/blob/master/README.md that you may find useful. Thank you for the great videos!
I ordered some of the RCWL-0516 to try at home. If the microwave circuit is a regenerative receiver, it will transmit as well as receive. This was a problem with early regenerative receivers, they interfered with other receivers and could be detected easily. These may be detecting motion by moving objects interfering with the regeneration.
Thank you for the video, Andreas! I love your channel! I want to report that the RCWL-0516 works great with the Sonoff Basic switch with the OUT pin on the Sonoff's GPIO14 pin and the 3.3V pin connected to the 3.3V of the Sonoff. I use it to report movement via MQTT.
I just found your channel, great video! I like how precise and concise your comments are. Brief, clear and to the point. You have a new subscriber! And you made me laugh so much at the end when you said "If true then like". 🤣
Genial! Justo acabo de comprar el RCWL-0516 para detectar la presencia de intrusos, una muy buen explicación amigo! Gracias por compartirlo con nosotros
Hi Andrea thank you for the efforts in reviewing the sensors. For the proper working of the sensors perhaps you can cross check the hypothesis put by sirus o your spectrum analyser. The signal should be visible in the UHF band, based on the geometry of the antenna on the PCBA.
Great video. Appreciate the effort to examine and compare the most important characteristics of each unit with a scientific approach. I agree with you, even if the units are simply measuring the variance in transmitter output to determine motion, some sort of return circuit is required. Thanks again.
Nice introduction in Mircorwaves. I like your channel very much.Also becaues you are a swiss guy too :) It's very nice to see, that we have such brillant heads in our small country ;) Since 3 days I played around with the RCWL-0516 and I'm very happy with it. Stay healthy and I hope a lot more videos are coming up :) Next I want to build a LoRa Gateway because in my region no one have it. A liebe Gruess und sunnigs Wätter :)
@@AndreasSpiess Gerne, mache ich gleich mal :) Herzlichen Dank für den Link! Was ich wirklich so toll an deinen Videos finde ist, dass du es auf eine Weise rüber bringst, die selbst ein nicht-Elektroniker daraus schlau wird. Dafür ein herzliches Dankeschön. Behalte dein way-to-do bei, denn dieser ist wirklich genial. Schönes Wochenende und herzliche Grüsse aus Bern
Just found your channel.. Great work! I appreciate the comprehensive analysis of these cheap sensors, as the ebay listings tend to give little information.
I was looking for one of these devices to use in the UK for remote security applications. After looking around there was one company who could supply a module which could detect at 75m, (people/vehicles) with current draw down to 1mA. Not really cheap but top quality. You can also purchase ready to go radar speed camera, with a warning sign: slow down, over 20mph, etc. I never knew these devices were available to the general public but they are.
There is one of those speed signs at the local retirement village, indicates your speed either in flashing red or green. What is *really* cute, is that it detects *direction*, indicating only traffic approaching, not departing. That requires somewhat more sophistication.
At 3:23 - this is actually 'super-regenerative' RECEIVER, which has bad properties of emit signal at the reception frequency. Reflected signal from moving object is shifted in frequency and phase, and it detects doppler shift in frequency spectrum by mixing emitted signal with received. The product of mixing is amplified and send to the detector circuit.
I'm not sure a superregen is the correct term. Essentially, it is merely a continuous wave oscillator tightly coupled to the antenna (in fact, the antenna itself is the tuned circuit) so that small changes in the "Q" are detected in the running current. It is in fact, monitoring the standing wave patterns is sets up in the environment so even the term "Doppler" is not 100% illustrative (as it probably detects sideways movement to some extent as well). Note that its frequency is not necessarily stable either; it will be de-tuned slightly as the environment changes. And these are not new - they have been around for at least 40 years to my recall. What is recent, is the ready availability of microwave transistors and stripline PCB manufacture. The ones 40 years ago operated in the upper tens or low hundreds of Megahertz with the transistors then available and used correspondingly dimensioned whip antennae. And because they necessarily detect small fluctuations in the current of the tuned circuit, all such designs *must* incorporate an effective regulator and it would be inappropriate to bypass this unless your alternative source was itself well regulated - and separate from other loads such as - the microcontroller.
Hello, I am a radar systems engineer for 30 years. It looks like the antenna is a double-dipole and is intended to mount in a simple tube-like cylinder. In this mode it would be a simple motion detector which is what you said correctly at the beginning of the video. However the price is amazing and I will get some of these for proximity sensors around my home as the basis for a new security system. I am also subscribing to your channel. Thank you very much for this video!
Great to have such subscribers! Is this simple design with only one transistor something you know? Because so far, nobody was able to explain us how it works and which principle it uses. For example, I was able to prove, that the modules work ok even if other modules are in close proximity. But as soon as I switch one module off or on, the others trigger. Another question is, if it senses speed and in which direction (from-to or also across). I did not do any proper tests about that.
Yes, with a common ground signals can go in both direction on a wire in TEM mode, so TX mode signals to from the XO to the TX transistor, received signals go the other direction, through a circulator and into the RX front-end, in this simple setup harmonics and distortion are ignored since this is a simple switch motion/no motion based on Doppler signal which is what you said. These modules seem to be in the 5GHz band that is internationally not regulated it is the "other" ISM band that very few can use because of lack of range. In this case that is positive attribute since range-to-target is so close. For several units close together yes there is interference but since the unit only detects Doppler. It is like saying one unit can use another unit's TX signal as long as there is no motion. The other units trigger when a unit is switched off because they detect a change in this signal when a unit goes down the XO does not stop abruptly but changes frequency as power is removed and voltage from the power supply capacitor sags. That is what the other units are detecting.
Very good, thanks. Have you thought about using aluminium foil, say placing your module in a project box lined with foil on the sides but with "clear" lid? This should give a crude ~120° cone sensitivity.
I think the lack of interference between 2 modules can be explained by them giving out a short pulse on a interval and only listening for a very short period after the pulse, making it unprobable that a sensor will be listening while the other is transmitting
I doubt that this is the case as we have not enough active components on the board. There are many discussions and videos which try to explain how they work. I do not know exactly.
My project with these OWL sensors as a movement sensor, with an ESP8266 to send data, was frustrating with false signals and unreliability until I ensured the WiFi was OFF for most of the sensing time loop while movement pulses were counted and only turned on briefly to transmit the counts! Results:= lower current draw and great reliability. Not surprising but it look time for me to figure that out. Thanks for your inspiration.
Thank you for sharing your experience. Looking at the Spectrum analyzer in my newest video you saw that they work around 3 GHz. Which is very close to 2.4GHz Wi-Fi. So it is no wonder that you get cross-talk.
Great video. I was hoping they would be more directional to replace my PIR sensors (I need them to distinguish between movement in my corridor vs inside a room), and now I'm considering creating barriers using glass.
There are two active devices in the RF line up, the oscillator and a mixer diode. The oscillator generates the transmit carrier. There are two signals in the mixer diode, the transmit carrier and also the reflected signals coming back from the room. If there is any movement in the room, the reflected signal at the mixer diode will be different from the transmit carrier (a doppler shift), and a Ftx-Frx differential will be produced out of the mixer diode - this usually at audio frequencies.
There are a few theories below in the comments. It is not clear if the Doppler effect is used. Another probable effect is phase shift. But I do not know.
I think that transistor is used as antenna switch which is used to multiplex transmitter signal and receiver signal to switch over for particular time and hence same antenna can transmit and receive the rf signal
@@AndreasSpiess it depends on circuit designer but according to me single transistor can also be used to transmit or receive through common antenna for example if this transistor is off then it will work as transmitter if it is on then it will work as receiver.
I wanted to combine the RCWL-0516 with some cheap 433 sender with a fixed codes but the problem with that setup is that the 433 sender is producing the signal when I manually or by the RCWL cut off the power, right in that moment which is weird. It probably stores some power in its coils or caps...
Just watched your video, good job. I would like to know if any of these operate in the Ku band and could have a transmitter range of over 1/4 mile around 5/8 kilometers. These would be great fun to mount on your front bumper and drive down the highway setting off radar detectors.
Great video. Never new these existed. Would be interesting to see a video demonstrating when to use either radar, ir or microwave sensors. Also, would be great to see what can be achieved with them, like can the device give a different reading dependent on proximity
I just bought 5 of the RCWL-0516 from a supplier on Amazon. I tried 3 of them with 5v on 'VIN' and a LED + CL Resistor on 'OUT'. All of them only manage to detect my movement at distance of 2 cm (with my finger)! I had to snap the boards free - so perhaps I managed to buy a faulty batch.
Hi Andreas, I only comment now (quite a while after watching this for the first time). I got myself 10 RCWL-0516 sensors and I just LOVE them. I automated my lights in both my house and workshop. I even made an alarm sensor unit to monitor movement at my main gate. Thanks to this unit I was able to catch two thieves in the act of trying to break in (South Africa has very high crime rate, so you need to do anything possible to give you an early warning) I did however found that if you are running the RCWL-0516 over a long distance you need to add a PI filter. Two big sized capacitors (100-470uF) with a 10ohm resistor in series (two caps ground tied to ground, one cap receives the supply power, resistor in series to the next cap positive and that goes to VIn of the RCWL. That completely eliminated any false alarms. The unit is very sensitive.It picks up small animals such as pigeons and cats. Oh, and watch out for FOG. Moving moisture seriously affects the unit. That was the only time it failed (false alarms). So for people living in high fog areas, sorry, this will not work. Thanks for a great channel. Love your work. Keep it up.
Thanks for sharing your experience. I did not know about the fog. And maybe it would help to have two sensors in the same area to distinguish between small and bigger "animals". Only if both see something it is big enough.
Hello again, I found that these units are quite sensitive. I do have two units spaced about 6 meters apart (my original idea was to detect direction of movement). That works but it senses both human and small animals (i.e. the neighbors cat) with the same accuracy. I programmed my Arduino Nano to now count the number of triggers or monitor the duration of how long the unit is triggered before creating an alarm. This did eliminate many false animal triggers, but if the little critter decided to hang around the sensor, unfortunately then the alarm goes off. My HD Closed circuit camera system is then used to confirm friend (small animal) or foe (real criminal)
Yes, it worked for me in the hall all right but not in the bathroom, when I kept the unit on a plastic drum full of water. Somehow the effect was dampened and worked only within a few cm as opposed to 3-4 m in a open dry hall.
As many commenters rightly found out, these devices are regenerative receivers. If you are interested in "real" radar sensors, I propose watching video #439
If these devices are regenerative RECEIVERS do they need a licence? After all, they do actually radiate! thanks
@@andrewainger I do not think a license would help here. They are anyway illegal...
excellent comparison video, I can see allot of work went into making this.
Thanks!
Lucky for him that his neighbour works as a ground controller at the local airport, so he's an expert at flapping his arms around :-P
Mystery gadgets! Nice writeup. You have a very comfortable voice and clear, easy to understand diction. Good job!
Thanks!
Ketil Duna , Really good diction, I'm from Russia and I understood all the information. Good work!
Today my RCWL-0516 's arrived from ali-express, could'nt wait to do some experiments .. (did'nt add any additional components)
Wow .. these things are unbelievable sensitive especially moving to or away from them. Over the entire distance of my buro (~4 Meter) a movement of 2 cm's of my hand is enough to trigger it.
Thanks a lot Andreas for making this great video!
You are right. Most of the time, I think, we have to reduce sensitivity rather than to try to increase it...
They are really too sensitive. I tried connecting one(rcwl-0516) to a nodered counter node via a 8266 microcontroller to detect the number of detections and found that even with nobody present in the apartment it is still detecting movement at times.I live in an apartment building so I assume it is detecting movement through the walls in the other apartments.I did not try to reduce the sensitivity yet. Has anybody tried it with resistors to reduce sensitivity?
Sir your videos are gold, it reflects how much work you put into these masterpiece review videos.
Thank you!
I have been using RCWL-0516 Microwave Radar Sensors in a smart lighting application (integrated with ESP32 developer boards) for several months now. To this video I would add a couple notes. The first is that though the sensors do not interfere with each other, they can get false triggered from the ESP32. This effect falls off after a centimeter or two. Lesson learned, be careful mounting the sensors to the same circuit board as your controller. The lack of directionality and ability to penetrate wood is amazing and perfect for my application. The sensors often detect me just before I enter the rooms with my lights.
My sensors appear to work through regular glass. I mounted some of my smart lights on my double pane window and the detectors see me from outside my house. My different experience may be explained by the sensors penetrating the wood but it may be that I’m using traditional glass and your video reported testing against acrylic glass. The later makes sense as acrylic would act more like water than silicate.
A final note on voltages... Though it does take 5V to power the sensors, the sensor output voltage is 3.2-3.4V. This is perfect if you’re powering your circuit with a 5V supply and reading the signal with a CMOS device like the ESP32.
Thank you for your additions!
Will it be able to detect u if ur are not moving or sleeping
Thank you so much for doing this, prior to this video I was not aware of these cheap radar sensors (the rcwl-0516 is on eBay for about a dollar). As usual your testing was detailed and your explanation was perfect. Another excellent video!
Thank you for your nice words!
I keep repeating myself... great video !
A very good comparison which is very usefull. It will defenately help me
for choosing the right one.
Thanks Andreas !
You are welcome!
Thanks for checking out these various sensors. I think I will find them very useful and it is great to be able to rely on you to sort the features of the many choices available!
You are welcome!
Hi. I've recently discovered the RCWL-0516 and in search of more specifics I've then found your video.Your extensive tests are very helpful. Especially the needed voltage to run it, the diagnosis if the devices interfere with each other, the directionality and what they penetrate.
Viele Grüsse aus dem Hackerspace Ruum42 aus der Ostschweiz.
I discovered those modules recently, and still waiting for them to arrive. You saved me a lot of time, i don't have to make a comparative test. Thank you
You are welcome!
First of all, great video! These motion detection radars most likely works in doppler mode, which is sensitive to frequency close to its emitting frequency, which explains why 2 of the same model do not interfere with each other, and why they don't detect stationary object.
You are probably right. There are a few ideas around in the comments. I do not know what is right or wrong...
Andreas Spiess, you are putting out very good content. Thank you! You are having an impact on the world.
Nice to read. Thank you!
Perfect timing! I just received four RCWL-0516 units. I could not decide which variety to get and it appears randomness intervened to select a good choice for me.
These evaluations of similar products are both interesting and useful. Thank you!
You are welcome!
Very good, thank you.
You have to bare in mind that a lot of double glazing windows have an aluminium coating all over the glass for thermal insulation/reflection, and so this will no doubt explain away a lot of the RF attenuation you found when doing the double glazing window through tests.
Maybe it has a coating. But I do not think so. It is more than 20 years old and back then, coating was quite expensive.
IRC these units don't work like a radar. IRC they don't receive a signal back from what they send out. They just emit a continuous wave and monitor how much power it is using to transmit. if something moves in it's "field" it changes the SWR standing wave ratio of the transmitter, causing it to us more or less power that the comparitor uses to cause a trip.
This is one additional opinion on how these devices work. I stopped to try to understand. I just use them...
Baaaa
I agree with Sirus. This is very similar to the way shop lifting alarms work.
Depending of the distance between the transmitter and the reflections the signal arrives at the receiver either in phase, out of phase or in betwee at the receiver. The two signals are present on the transistor at the same time. As the transistor is a nonlinear device the two signals mix together and generate a DC offset dependant of their relative phase. When an object is moving in front of the sensor this DC offset oscillates at a very low frequency. This signal is amplified and detected by a chip which is very similar to the BISS0001 used in PIR sensors as the output signals of these sensors are nearly identical. The only difference is that this chip includes a built in 3.3v regulator.
@@keesterwee4890 They do not work the same way as the shop theft systems. They rely on the same technology used with prox or access control tags. The arches transmit an rf signal that sweeps a small bandwidth at around the 3.8ghz mark. The tags on the shop item have an antenna tuned to that frequency, a small capacitor and transistor in a smc package connect to the antenna. The RF energy from the arches powers the IC in the alarm tag and creates a simple oscillation resulting in a reflection of RF power at a slightly offset frequency or delay depending on the system type. The signal return to the arch triggers the alarm.
It's just come over to the uk but stores in Japan have been using this for years with IC's that will return a pulsed code instead of just a "present" signal as with the theft alarms. These shops in Japan allow you to swipe your customer card and then go round the store filling your trolly. When you exit the store all the prox codes are read and you are billed for the goods. Sadly until all the packaging manufacturers and the industry incorporate smart IC technology we cannot switch to this system.
I tested a product with a smart tag a while back and was not surprised to discover that the coded return from the product matched the bar code ! I assume this has been done to make life easier for any stores that have a barcode database. They only then need switch from a barcode reader to an RF based one. I can't see unmanned stores taking of in the UK just the stock itself ;-)
With regards to how these little detectors do operate see my reply to "Sirus"
Thanks Andreas, I always enjoy your videos.
You are welcome!
Excellent details. Thank you. It will be great if you can make a video on using those as metal detectors! Like detecting metal hidden underground or maybe behind a large lump of sand. Those treasure hunters will love the video :)
Thanks for the feedback. Maybe I will try it once...
Unless the ground is dry, wouldn't the moisture swamp the return signal?
The long awaited radar sensor comparision you promised to do! You have not forgotten it! Now I know these devices work and which one to buy. Thank you so much!
You are welcome!
Andreas,
The working principle of these type of radars (radio detection and ranging) is well understood and used in many applications already for many years.
In a nutshell:
These radars typically work in the L to X band : 1GHz-12.5GHz
They are frequency modulated continuous waves radars typically with linear frequency sweeps, say 100Mhz
Example: a saw tooth frequency of 100kHz changes the frequency linearly from 2.4GHz to 2.5GHz in 10 microseconds
The transmitted signal is sent into the world via the antenna
The received signal that bounced back from an object on a distance d from the antenna is received back with a delay of 2d/c seconds (c speed of light 3*10E8m/sec).
Example: if d is 3m, the delay is 20 nanoseconds. During this delay the frequency of the transmitter has increased 200kHz versus the received signal. (100MHz*20nsec/10usec)
The transmitted and received signal are combined (mixed) and passed through a highly nonlinear element, i.e a diode. The output of this process are waveforms that include the sum and difference of the 2 signals and their harmonics
Through proper filtering we can isolate the frequency difference (200kHz), calculate the delay (20 nsec) and the related object distance (3m)
Kind regards
Thanks for your explanations. I only doubt if or how all these functions can be done with only one active component. That is the miracle for me...
If you look at a newer video we use the principles you mentioned for a bicycle counter. But this device will have much more parts.
Dude - did you copy that out of a textbook? Nice explanation for doppler ranging radar. But that's not what this does. It just detects motion by mixing the transmitted and received signals together and detects a low-frequency beat. No ranging info. No speed info. Just detects motion.
That is not the principle how these work, though. They are simple regen style recievers
Good video. I like how you compared these units and gave a clear overview of their main advantages. (Good to see I picked the right one when randomly ordering the cheapest radar-sensor I could find). Thanks!
You are welcome!
thank you for your effort. this was interesting AND useful!
Thanks!
Super Vergleich! :) Die Neugier auf die Module ist geweckt und alle wichtigen Fragen sind in einem Video beantwortet! Klasse Arbeit!
Danke!
"of course the technology can also be used against us" LOL
:-)
Excellent! Very professional and comprehensive. Saved me tons of work... and money! Thank you, Andreas. I'm looking forward to your next video.
Thank you for your feedback!
@Andreas, some new LiDAR models entered the market, you could test them maybe?
Any links?
This one is the original of the cheaper LiDARs on the market but currently sold out: www.3dxr.co.uk/product/benewake-tfmini
America: www.seeedstudio.com/Seeedstudio-Grove-TF-Mini-LiDAR-p-2996.html
America 2: www.robotshop.com/en/benewake-tfmini-micro-lidar-module-12-m.html
This one is a China knockoff but perhaps the same: www.aliexpress.com/item/RCmall-Lidar-Range-Finder-Sensor-Single-Point-Micro-Module-for-Arduino-Pixhawk-Cable-Benewake-TFmini-Drone/32852024277.html
High Quality LiDAR for reference (older) : www.robotshop.com/en/lidar-lite-3-laser-rangefinder.html
Thanks for your links. I will look into the matter.
Thanks for this comprehensive and systematic comparision. It comes very handy to me because I also received a sensor similar to XYC-WB-D1 for playing around and looking for a helpful application. Unfortunately (?) most helpful application are already covered in my environment.
It is really an excellent work to do all that with just one (1) transistor and some passives. Chapeau!
That is what I think, too...
I don't usually like videos on request, but I had to make an exception.
Thanks for liking. I hope, I did not request it. I just know, that many people forget it..
Thank you for your thorough analysis of the devices. A fine video presentation of your results.
You are welcome!
With outstanding content like this, it's really a crime that AS doesn't have 200,000 subs. Soon, I trust!
Thanks for the nice words!
Are Jayem
He's speaking to a specialized group with this subject matter. He is very good at what he does, but there are not many who have an interest in sensors.
Besides the particular topic (sensors) - which is gaining traction with many makers and electronics diy hobbyists - I find a good number of our host's presentations balanced, informative and accessible, and creatively interesting. By doing this, what would be specialized subject is delivered for a wider audience to ponder and spark ideas.
Are Jayem
I definitely agree with you.
Andreas , Thank you for your articulate understanding of this technology.
You are welcome!
Cool stuff. I might buy a few to play with
:-)
You continue to read my mind and post the videos just when I need them. Thanks
:-)
I bought a sensor which is marked "2.7GHz" from Aliexpress and was quite surprised by the spectrum of signal which it emits. It is not a narrow "spike" but rather wide, maybe 1 MHz wide. Is that happening because of poor Q of PCB resonator?
I do not know, because I was not able to see much spectrum below 3 GHz.
1 MHz isn't that bad for these type of devices.
with an arduino your frequency can vary as much as 0.5% - at 3 GHz that would be 1.5 MHz just from inaccuracy.
Thanks for taking the time to run through these. Wish I had found this video before I bought 5 of each of the RCWL and HFS boards. I need 3 working units (always buy extra from China). Looks like the cheaper boards will be the best fit. NBD. At the prices these things are going for these days I can throw the others in a drawer to use for something else some day. The HFS boards will be better if I need something to be directional.
I hope they will work for you. Keep the power lines very clean (there are a few discussions about that)
Are you sure the RCWL-0516 does not work on 3.3V? I really cannot see a reason why it shouldn't work if you power it with 3.3V on the 3.3V pin. Usually a voltage regulator doesn't care much if you power its output with the right voltage and no input connected... Even if the voltage regulator is integrated within the IC. And I don't think the unregulated input voltage is used anywhere else except on the voltage regulator input. You should try it.
You are right. I tried it again now and it works. I do not know what I did last time... BTW: I did not see a voltage regulator chip on board.
@Roter . If I understand you well, the 3.3V pin can also be used as an INPUT (on +3.3V) as long as the Vin pin is not used ... am I right ?
Yes
Thanks, then I'll try to power the radar sensor from the 3.3V output of my ESP8266 board.
Yann M I'd like to know how you get on.
Movement is almost never detected by the red shift (frequency change) of the reflected radio wave. Speed is measured in a totally different way, with a so-called doppler radar. Doppler radar measures the distance of an object by measuring the time elapsed between sending out and receiving the same signal. It sends out two singals, and measure the change of distance between those two signals.
I think there is a misunderstanding here? The RADAR I was working on cost just under £2,000,000 and use multiple pings etc. However, I understand these very low-cost units operate exactly as described in the video. I purchased mine for
Hello Andreas,
Before I begin, I like your videos a lot.
In your video at 15:04 min. you explain that the RCWL-0516 cannot work in a 3.3 volt environment, I make a mistake and put 3.3 volt as input voltage.
So 3.3 volt on the 3.3 pin and GND on the GND pin then a diode connected on the Out pin and GND, and wonder the RCWL-0516 works also, it detects movements like before.
I think that you can use the module from 3.3 volts and if you have 4 volts till 28 volts you must connect the input voltage on the VIN pin.
www.elecrow.com/rcwl-0516-microwave-radar-sensor-switch-module-body-induction-module-4-28v-100ma.html
Greetings from Holland,
Jan-Henk van Kesteren
Thanks for your link. Maybe there are different versions of the same modules around, as in many other cases. Or I did something wrong, which also happens from time to time.
Top notch video. Practical, succinct, objective. A benchmark for review vids.
Thanks! :-)
Great video Andreas!
I found this GitHub repo that has a schematic of the RCWL-0516 : github.com/jdesbonnet/RCWL-0516/blob/master/README.md that you may find useful. Thank you for the great videos!
Thanks for your link!
I thought youtube didn't allow links in the comments?
I ordered some of the RCWL-0516 to try at home. If the microwave circuit is a regenerative receiver, it will transmit as well as receive. This was a problem with early regenerative receivers, they interfered with other receivers and could be detected easily. These may be detecting motion by moving objects interfering with the regeneration.
Well possible. BTW I built such a (tube) regen receiver in another video...
The 1.8 GHz could be a DECT phone
Thanks for the hint. This is well possible because one was close by.
Thank you for the video, Andreas! I love your channel!
I want to report that the RCWL-0516 works great with the Sonoff Basic switch with the OUT pin on the Sonoff's GPIO14 pin and the 3.3V pin connected to the 3.3V of the Sonoff. I use it to report movement via MQTT.
Thank you for your feedback. I am sure it will help other viewers!
Great hands-on test ! Thanks !
More info here: github.com/jdesbonnet/RCWL-0516
Thanks for the link.
Thank you very much. Appreciated.
Thorough review that answered all my questions.
Thank you!
Awesome! I have been waiting for this video since you mentioned it in one of your mail bags, thanks for coming through with the usual great content.
Thanks!
I just found your channel, great video! I like how precise and concise your comments are. Brief, clear and to the point. You have a new subscriber!
And you made me laugh so much at the end when you said "If true then like". 🤣
Welcome aboard the channel!
Genial! Justo acabo de comprar el RCWL-0516 para detectar la presencia de intrusos, una muy buen explicación amigo! Gracias por compartirlo con nosotros
You are welcome!
Hi Andrea thank you for the efforts in reviewing the sensors. For the proper working of the sensors perhaps you can cross check the hypothesis put by sirus o your spectrum analyser. The signal should be visible in the UHF band, based on the geometry of the antenna on the PCBA.
Their frequency is above the limits of my SA :-(
Excellent comparison Andreas. I will be using in my future projects.
Thanks!
this video was incredibly informative! Keep it up, man
Thanks!
Great video. Appreciate the effort to examine and compare the most important characteristics of each unit with a scientific approach. I agree with you, even if the units are simply measuring the variance in transmitter output to determine motion, some sort of return circuit is required. Thanks again.
You are welcome!
I very like your videos and how you do explain the comparison. You're now my favorite youtuber.
Thank you and welcome to the channel!
Very nicely done - appreciate your thoroughness on the testing; gave me some background on what they might do.
Thank you!
Very useful comparison video . Great effort is done .
Thank you!
Nice introduction in Mircorwaves. I like your channel very much.Also becaues you are a swiss guy too :) It's very nice to see, that we have such brillant heads in our small country ;) Since 3 days I played around with the RCWL-0516 and I'm very happy with it. Stay healthy and I hope a lot more videos are coming up :) Next I want to build a LoRa Gateway because in my region no one have it. A liebe Gruess und sunnigs Wätter :)
Wenn es dich interessiert kannst du hier mal reinhören: www.srf.ch/sendungen/digital-plus/ue60-influencer-landet-grosserfolg-mit-elektronik-videos
@@AndreasSpiess Gerne, mache ich gleich mal :) Herzlichen Dank für den Link! Was ich wirklich so toll an deinen Videos finde ist, dass du es auf eine Weise rüber bringst, die selbst ein nicht-Elektroniker daraus schlau wird. Dafür ein herzliches Dankeschön. Behalte dein way-to-do bei, denn dieser ist wirklich genial. Schönes Wochenende und herzliche Grüsse aus Bern
Vielen Dank!
Congratulations for your work. This type of videos are very useful when making a purchase decision.
Thank you!
Nice work. It was pleasure to watch. Many thanks.
Glad you enjoyed it
thank you so much for doing this test its very important for many useful applications !
You are welcome!
Just found your channel.. Great work! I appreciate the comprehensive analysis of these cheap sensors, as the ebay listings tend to give little information.
Thank you!
Video was very interesting to watch and the comments contained more interesting information, subscribed.
Welcome to the channel!
I was looking for one of these devices to use in the UK for remote security applications. After looking around there was one company who could supply a module which could detect at 75m, (people/vehicles) with current draw down to 1mA. Not really cheap but top quality. You can also purchase ready to go radar speed camera, with a warning sign: slow down, over 20mph, etc. I never knew these devices were available to the general public but they are.
There is one of those speed signs at the local retirement village, indicates your speed either in flashing red or green.
What is *really* cute, is that it detects *direction*, indicating only traffic approaching, not departing. That requires somewhat more sophistication.
I think, these devices work with a different principle, because they can also measure speed.
At 3:23 - this is actually 'super-regenerative' RECEIVER, which has bad properties of emit signal at the reception frequency. Reflected signal from moving object is shifted in frequency and phase, and it detects doppler shift in frequency spectrum by mixing emitted signal with received. The product of mixing is amplified and send to the detector circuit.
I'm not sure a superregen is the correct term. Essentially, it is merely a continuous wave oscillator tightly coupled to the antenna (in fact, the antenna itself is the tuned circuit) so that small changes in the "Q" are detected in the running current. It is in fact, monitoring the standing wave patterns is sets up in the environment so even the term "Doppler" is not 100% illustrative (as it probably detects sideways movement to some extent as well). Note that its frequency is not necessarily stable either; it will be de-tuned slightly as the environment changes.
And these are not new - they have been around for at least 40 years to my recall. What is recent, is the ready availability of microwave transistors and stripline PCB manufacture. The ones 40 years ago operated in the upper tens or low hundreds of Megahertz with the transistors then available and used correspondingly dimensioned whip antennae.
And because they necessarily detect small fluctuations in the current of the tuned circuit, all such designs *must* incorporate an effective regulator and it would be inappropriate to bypass this unless your alternative source was itself well regulated - and separate from other loads such as - the microcontroller.
That is possible too. Thanks for the correction.
Maybe you have a look at the comment of Alejandro Vargas below
Датчик движения RCWL-0516
Время задержки включения будет:
T = 245 x CTM, Где CTM - в МкФ, T - в секундах
Hello, I am a radar systems engineer for 30 years. It looks like the antenna is a double-dipole and is intended to mount in a simple tube-like cylinder. In this mode it would be a simple motion detector which is what you said correctly at the beginning of the video. However the price is amazing and I will get some of these for proximity sensors around my home as the basis for a new security system. I am also subscribing to your channel. Thank you very much for this video!
Great to have such subscribers! Is this simple design with only one transistor something you know? Because so far, nobody was able to explain us how it works and which principle it uses. For example, I was able to prove, that the modules work ok even if other modules are in close proximity. But as soon as I switch one module off or on, the others trigger. Another question is, if it senses speed and in which direction (from-to or also across). I did not do any proper tests about that.
Yes, with a common ground signals can go in both direction on a wire in TEM mode, so TX mode signals to from the XO to the TX transistor, received signals go the other direction, through a circulator and into the RX front-end, in this simple setup harmonics and distortion are ignored since this is a simple switch motion/no motion based on Doppler signal which is what you said. These modules seem to be in the 5GHz band that is internationally not regulated it is the "other" ISM band that very few can use because of lack of range. In this case that is positive attribute since range-to-target is so close. For several units close together yes there is interference but since the unit only detects Doppler. It is like saying one unit can use another unit's TX signal as long as there is no motion. The other units trigger when a unit is switched off because they detect a change in this signal when a unit goes down the XO does not stop abruptly but changes frequency as power is removed and voltage from the power supply capacitor sags. That is what the other units are detecting.
Thanks for your explanations!
Very good, thanks. Have you thought about using aluminium foil, say placing your module in a project box lined with foil on the sides but with "clear" lid? This should give a crude ~120° cone sensitivity.
If you look at other comments: This should work. Of course, it depends on the application.
Hello Mr Spiess, that noise at 1800Mhz that you labeled is a GSM band used by the telecommunications industry, it’s known as DCS-1800 or B3 LTE
Thank you!
Great video as always. Thanks Andreas. Have a great Sunday!
Thanks. You too!
Thank you and your neighbour as well for this demonstration of these interesting devices ;-)
:-)
Great video. FWIW, I'm using 3.3v input via Arduino on the RCWL-0516 with no problems, so it is definitely the sensor of choice for me.
Thanks for the feedback.
This is very helpful video Andreas. Nicely done.
Thanks!
At 0:50 on this video, can anyone tell the polarization of the big radar? Vertical, horizontal, circular?
I must thank you for these videos, they are great.
You are welcome
Very nice comparison, Andreas!
Thanks!
Thanks for your video. I need to use motion detection for my project. I appreciate your effort and infos.
You are welcome!
I recently got my hands on the RCWL-0516 and I found that supplying 3.3V to the 3V3 pin allowed the module to basically work of 3.3V!
Thank you for sharing!
A very comprehensive review! Thank you for your hard work!
You are welcome!
Many thanks for the great summary - exactly what I needed to know :) Best regards from DE
You are welcome!
I think the lack of interference between 2 modules can be explained by them giving out a short pulse on a interval and only listening for a very short period after the pulse, making it unprobable that a sensor will be listening while the other is transmitting
I doubt that this is the case as we have not enough active components on the board. There are many discussions and videos which try to explain how they work. I do not know exactly.
i`m from Brazil, your explanation is excellent, congratulations and thank you
You are welcome!
Fantastic video. you are as thorough as ever. thanks for your big use off time to make this video 👍😀
Thanks for your feedback!
Never heard of those fantastic little radar sensors. Thank you.
You are welcome!
My project with these OWL sensors as a movement sensor, with an ESP8266 to send data, was frustrating with false signals and unreliability until I ensured the WiFi was OFF for most of the sensing time loop while movement pulses were counted and only turned on briefly to transmit the counts! Results:= lower current draw and great reliability. Not surprising but it look time for me to figure that out.
Thanks for your inspiration.
Thank you for sharing your experience. Looking at the Spectrum analyzer in my newest video you saw that they work around 3 GHz. Which is very close to 2.4GHz Wi-Fi. So it is no wonder that you get cross-talk.
Great video. I was hoping they would be more directional to replace my PIR sensors (I need them to distinguish between movement in my corridor vs inside a room), and now I'm considering creating barriers using glass.
Maybe you can increase directionality be shielding the rays with metal sheets?
There are two active devices in the RF line up, the oscillator and a mixer diode. The oscillator generates the transmit carrier. There are two signals in the mixer diode, the transmit carrier and also the reflected signals coming back from the room. If there is any movement in the room, the reflected signal at the mixer diode will be different from the transmit carrier (a doppler shift), and a Ftx-Frx differential will be produced out of the mixer diode - this usually at audio frequencies.
There are a few theories below in the comments. It is not clear if the Doppler effect is used. Another probable effect is phase shift. But I do not know.
Thanks for all the hard-won information! Great study.
You are welcome!
Interesting video which gives a lot of useful information about these devices.
Glad you think so!
I think that transistor is used as antenna switch which is used to multiplex transmitter signal and receiver signal to switch over for particular time and hence same antenna can transmit and receive the rf signal
I am not sure. Where would then be the transistors for the receiver and the transmitter?
@@AndreasSpiess it depends on circuit designer but according to me single transistor can also be used to transmit or receive through common antenna for example if this transistor is off then it will work as transmitter if it is on then it will work as receiver.
I wanted to combine the RCWL-0516 with some cheap 433 sender with a fixed codes but the problem with that setup is that the 433 sender is producing the signal when I manually or by the RCWL cut off the power, right in that moment which is weird. It probably stores some power in its coils or caps...
Strange.... I hope you will find the error.
I use the RCWL 0516 with a LiIno Cell and it works down to 3.3V if you use the Vcc as Power In.
Thank you for the information!
Fantastic review, full of useful information. I must get some of these to play with once I have finished refurbishing my bathroom.
Best wishes
Arthur
Maybe then I also have some more experience with them...
I just come across one of those sensors and landed here after googling. Geat info!
Thank you!
Excellent video. I can better understand you than a native English speaker. Good job, keep going.
Thanks!
Just watched your video, good job. I would like to know if any of these operate in the Ku band and could have a transmitter range of over 1/4 mile around 5/8 kilometers. These would be great fun to mount on your front bumper and drive down the highway setting off radar detectors.
similar interest for another application. any solution in the meanwhile? thanks!
topic was new to me. very good video, very professional. good job
Thanks!
Great video. Never new these existed. Would be interesting to see a video demonstrating when to use either radar, ir or microwave sensors.
Also, would be great to see what can be achieved with them, like can the device give a different reading dependent on proximity
You can do your tests. these devices are not expensive ;-)
I recently did a video about the new 24GHz sensors, BTW
Wow, such a solid video - respect to You Andreas
:-)
I just bought 5 of the RCWL-0516 from a supplier on Amazon. I tried 3 of them with 5v on 'VIN' and a LED + CL Resistor on 'OUT'. All of them only manage to detect my movement at distance of 2 cm (with my finger)! I had to snap the boards free - so perhaps I managed to buy a faulty batch.
I do not know your tests. You see how I tested them.
@@AndreasSpiess I just got a new batch of 5 units, today. The first two I tested are working fine (tested at a distance of 3m). I guess I was unlucky.
I didn't even know there are devices like these out there, but they seem pretty cool. The video was excellent, too.
Thanks!
Hi Andreas,
I only comment now (quite a while after watching this for the first time).
I got myself 10 RCWL-0516 sensors and I just LOVE them. I automated my lights in both my house and workshop. I even made an alarm sensor unit to monitor movement at my main gate. Thanks to this unit I was able to catch two thieves in the act of trying to break in (South Africa has very high crime rate, so you need to do anything possible to give you an early warning)
I did however found that if you are running the RCWL-0516 over a long distance you need to add a PI filter. Two big sized capacitors (100-470uF) with a 10ohm resistor in series (two caps ground tied to ground, one cap receives the supply power, resistor in series to the next cap positive and that goes to VIn of the RCWL. That completely eliminated any false alarms.
The unit is very sensitive.It picks up small animals such as pigeons and cats. Oh, and watch out for FOG. Moving moisture seriously affects the unit. That was the only time it failed (false alarms). So for people living in high fog areas, sorry, this will not work.
Thanks for a great channel. Love your work. Keep it up.
Thanks for sharing your experience. I did not know about the fog. And maybe it would help to have two sensors in the same area to distinguish between small and bigger "animals". Only if both see something it is big enough.
Hello again,
I found that these units are quite sensitive. I do have two units spaced about 6 meters apart (my original idea was to detect direction of movement). That works but it senses both human and small animals (i.e. the neighbors cat) with the same accuracy. I programmed my Arduino Nano to now count the number of triggers or monitor the duration of how long the unit is triggered before creating an alarm. This did eliminate many false animal triggers, but if the little critter decided to hang around the sensor, unfortunately then the alarm goes off.
My HD Closed circuit camera system is then used to confirm friend (small animal) or foe (real criminal)
Yes, it worked for me in the hall all right but not in the bathroom, when I kept the unit on a plastic drum full of water. Somehow the effect was dampened and worked only within a few cm as opposed to 3-4 m in a open dry hall.