Wired, not battery powered. There are 5 units in the house, all connected. The little status lights are all green.
Day before yesterday, one of the units in a bedroom was chirping and had a red light. I pressed the button briefly and that seemed to fix it - light went to green and it stopped chirping.
Now the main unit in the hallway is chirping about once every minute; this apparently started during the night. When it chirps, there is a little red light next to the green light that flashes at the same time. The green light is on all the time. I unscrewed the unit from the ceiling to see if I could see if there was a backup battery, but I didn’t find one.
I have tried pressing the button briefly, first once, and then several times in a row; I have tried holding the button down until the alarm goes off, and then turning the alarm off with the same button. Nothing has worked to get rid of the chirping.
I have a call in to an electrician but they haven’t called back yet.
It really sounds like a dead backup battery to me. On all my wired detectors the backup battery access is either on the non-wall side of the unit through a little trap door or there is a bay that swings out from the side with the battery in it. Maybe try looking the model number up and see if it has a battery backup, or user guide to diagnose the chirps.
Are you sure there aren’t back-up batteries that are dying. All of mine are wired, but all have back up batteries so that they will continue to work in the event of a power failure. The batteries still have to be replaced every year or so.
You didn’t mention how old the units were. That would help.
The back-up battery explanation seems feasible, but there’s another possibility. Ionizing detectors use radiation from an isotope of Americium. Apparently, it ionizes a sample of the air, making it conducive to electrical emissions. If there is particulate matter in the sample, it absorbs the ions and reduces the conductance. Since these operate all the time, it’s easy to imagine that after many years of use some of this equipment may wear out or become clogged. It might simply be time to replace them all.
Three years old doesn’t seem old enough that they should need replacing yet. Maybe give the problem unit a few good shots of compressed air to clear out any dust.
Like others have mentioned. There are probably backup alkaline batteries in them that need replacing. Mine are like that. I replace them periodically now during Daylight Savings.
If it’s not the battery (due to lack thereof) you might also try unplugging and replugging the chirping units (if they are connected via a modular connector and not just wired or soldered to the building power). A low battery would cause chirps warning of low power; similarly, a brown-out could cause a brief low-power situation just long enough (and/or low enough) to get the unit to panic and start chirping. Disconnection and reconnection could force a restart and get that chirp to stop (or it may simply resume once power is restored).
And, while you’ve got it in your hands, you might give it a blast of air to make sure the sensor is free of (three years worth of) dust.