Smoke Alarm, Hubcap or UFO?

UMMMM…I did the same many years ago. And same low point…Stupid now that I see them still in homes.

Just found my first one of these in a home yesterday I had an idea of what this was but thanks to this forum was able to confirm. These were in several rooms in the house along with the traditional smoke alarms. Home was built 1994.
I do remember when I was a kid back in about the early 70s my mother buying a couple of similar units but they worked on air and had 2 horns attached as I remember they also were activated by heat.

I have these and they are heat dectors. also if over a door can be used as an alarm. the disc in the center is same material on the nose cone of the space shuttles. bought mine in 1985. and for a 4 bedroom home, having them in the attic, over all exit doors, etc, cost me about 2500. they are the loudest alarms over doors ( we used fishing line tied to alarm and was hooked to door, if opened , the neighborhood heard it. saved our house from fire a few times. it detected a hot pan on the stove before a fire broke out.