Many do even if they are wired in. Could be the batteries, if it does have such, are getting old and need to be replaced.

I need to get off my arse tomorrow and go take a good look at it.

I think most of the hard wired units were done as new construction/remodel and most building codes require CO2

I tried to get the round mustard-colored plastic housing off the unit but only succeeded in prying it loose from its circular mounting bracket. Since I'm a klutz with mechanical things (who would have thought, huh), I didn't try very long to get the housing off the unit to check for a battery. I screwed it back into its mounting bracket.



It looks a lot like that one above, except a tad taller overall unit and mustard-colored. After I restored the AC power to it, everything was fine until today, when it squawked again. The WEIRD thing is, if the battery is dead or dying, why the hell would it not squawk every 15 minutes or so ? I can't see a battery in it so far, but then again I'm having to work at arm's length with it. Of course, I can't see a brand name yet.

I really don't want to break this thing accidentally.

ETA: I just restored the AC power to it, and it did NOT squawk at me at all. The red indicator light is lit inside the unit, so I'm assuming it's functional.

When the battery loses enough juice it will begin to squawk; fairly long intervals at first, with shorter and shorter intervals as the power decreases.
On ours, the light is green when fully functional.

It's mounted pretty high up on my living room wall, so it's really hard to do things with it without getting a really high stepladder. If mine is like yours, I'm guessing the battery is totally dead now.

The damn thing was a SMOKE DETECTOR, not fire alarm. It is so old, the company doesn't even list it on their website. There was no battery inside. It was a totally AC-powered unit.

It was a BRK Electronics 1769ACI smoke detector. I found an old manual to it, which states the possible problem:

They work by looking for something obstructing a gap (such as smoke). If they get some dust build up in the gap, they will falsely trigger. If it's been in place a long time, there could be a buildup in the sensor gap. They're not really difficult to replace, if you have a ladder and a couple of tools.

Good luck.