Alum Estate Fire Alarm model # 503 heat alarm (circa late 1960's/early 1970's)

This is the Alum Estate Fire Alarm. Although it is actually a heat alarm not a fire alarm. A very unique and rare piece circa late 1960's or early 1970's as I couldn't find date in the unit or box. It is set to go off when the temperature reaches 135 Fahrenheit (that's very hot). It has no batteries or wires but has two cylinder canisters inside that are filled with Freon gas. Once the Freon runs out the alarm will no longer sound. I have one other like this which is called a Latah fire alarm also model # 503 (from Latah Idaho). Definitely rare and unusual pieces. The box for this alarm is sadly not in the greatest shape but it came with mounting hardware (wall mounting), instruction manual and a business card. I was able to get some sound out of this. It as you can hear is a whistle chirp like sound. Not very loud except for the first time I tested it. But still a cool piece for a collection.