Can Anyone Identify This Old Smoke/CO Detector? Circa 1990

I have been going through my home to replace outdated smoke detectors. I have come across one, in the upstairs hallway that is clearly very old. I have Googled “ancient/ vintage smoke alarms and the closest thing I’ve found is here on the antique page. But nothing looks exactly like this.

Our home had a major remodel around 1990, so this is probably from that time. It is installed just outside a closet that contains our water heater.

The only markings are “do not paint”, plus it has a curious little bulb of what looks like mercury dangling down out of a port. There is also something that strangely appears to be a mini-USB port.

I hope I can connect the photos from my Google Drive account; I couldn’t figure out a way to upload pics directly to this blog.

I’m concerned that it might be something else… an old gas detector? Older CO detector? I assume it’s powered from the 120V AC. Any body think I can’t just yank it out of the ceiling?


Pete in Seattle WA

Go Hawks!

Making a few educated guesses. The little dangling bulb appears to be a thermistor. That is a resistor that changes value with temperature changes. That is being used as a heat detector which makes this a combination unit. The 3 cutouts around the thermistor are probably to clip in a protective cover for the thermistor.

What looks like a mini-USB is probably a test connection. Many older smoke detectors had a location where a voltmeter or a special meter can be connected to read the sensitivity of the device. Most likely the installer had a special cable to plug in to connect the meter. The little key way made sure the test cable was properly polarized when plugged in.

If it is operating on 120 volts AC, I recommend an electrician remove or replace it. That way you know the wires are properly terminated so nobody can get injured or your house burn down. If removing it, the box will need a proper cover to meet the electrical and building codes.

Picture of a thermistor below.

That looks like a Bosch detector.

I think 4j25 nailed it. Look at this link.

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The current version is a wireless device for connection to a security system. Do you have a security system? This may be part of it.

I see what appears to be a photoelectric chamber inside, so it’s likely a smoke/heat detector.

With that metal grating, it is more than likely an ionization type detector.

Thanks 4j25 and all. I DO have a home alarm system- it was probably state-of-the-art back in 1991, but we’ve never used it and it’s been unplugged. It had motion detectors and window magnetic things, so why not a smoke detector too? That would explain why there isn’t any obvious lights (system unplugged) and also why I can’t easily remove it from the ceiling (part of a “permanent” system).

The photo you posted is definitely my unit. I’m going out on a limb that the installers of the security system included a smoke detector to go along with everything else.

Mystery Solved!

Thank you FirePanel Forums!