Originally Posted by Maintenance 6
It's a heat detector. The house I grew up in had one in every room plus an annunciator and a test button in the upstairs hallway. Somewhere there should be a box with a large battery in it. Like a lantern battery. Probably installed 1950s.
I installed lots of heat detectors (rate of rise for fire alarms) but never happened upon one like this. Of course, in the 50's I was in high school.
It appears to have adjustable louvers. I wonder what the function of these would be.