Smoke Detector Question

[peterinwa]

I'd like to understand something about how my friend's smoke detectors work. We're all on vacation and heard from a neighbor that they went off and the fire department was called. They went into the house to be sure that everything was okay... it was, no fire.

We sent a friend over and they were still going off once in awhile. We told him to remove the backup batteries from each unit. He did this, and eventually they all stopped. We hope they didn't go off again sometime after he left!

The dectors are hard wired, and the batteries are only for backup in case of a power failure. What I don't understand is why taking the batteries out stopped them at all. And especially why it didn't stop them immediately, but they stopped after... well, I'm not sure but I'm guessing a minute later or so. I'd have to ask our friend that went to the home.

My friends will have an electrician check everything upon returning, but we'd love to understand why taking the batteries out stopped the alarms... but not immediately.

And maybe some thoughts about what might have caused them to go off in the first place.

Thanks so much!

Peter

[HayZee518]

loss of power would put the units into alarm mode - low battery "juice" would make the detector(s) chirp - also in alarm mode. restoration of power would start the alarm.

[peterinwa]

Thanks. I guess it's to let you know the battery has died.