Smoke detectors.

They are heat sensors. I have some exactly like that one. They do not have any batteries and operation is purely mechanical. They wind up with a special key. When the air heats up to 140 degrees (I think as I've had mine a very long time) the connectors holding the piece on the front melts and releases a spring causing a VERY loud alarm to go off for about 5 minutes. Mine are over twenty years old and still fully functional.

Yes these are called smoke detectors they do a similar job as smoke alarms except they are meant to connect to a type of panel ether a residential fire/burglar alarm panel or a dedicated fire alarm panel. When you replace them after ten years just like you would smoke alarms or if you ever have to remove them for something such as repainting be sure to disable whatever type of panel you have first before starting work. Failure to do so could result in fines.

Smoke detectors or heat detectors. Old looking ones.

They look like smoke detectors, electric type with battery back-up.

Jo Ann

I went and looked at a house and these were in every room on the first floor can someone tell me what they are.