The title is a bit vague, let me explain.
In my grandparents garage there is this device mounted high on the wall. It has a can of what my grandfather who was a fire chief said is air and that if it detects fire or heat (I cannot remember which word he used) would pierce the can and alert you. I do not have a photo of it. But I once did and I tried using google image search to find it, which usually works. But it came up with no results. I will include a drawing of what it kind of looks like. But their house was built in the 60s, not sure when the detector is from.
The best way to describe it is that if you look from the bottom it looks like a regular can of compressed air, the sides of the unit are white and the body has a design on it iirc. It is just a white box with no bottom, allowing you to see the can.
I will try to get a photo next time I visit. But that is hard to do without being noticed in fear of getting weird looks lol.
