A neighbor of mine has one of these smoke detectors that is powered by the wiring in the house(120 volt), with a 9 volt "back-up" battery. It beeps constantly(as the solely battery powered detectors do when their battery is low). I told her this and proceeded to take the detector loose from the ceiling, to change the back up battery. After I unplug it from the house wiring AND remove the 9 volt battery it still beeps. I put a known good 9 volt back into it and plugged it into the house wiring and it's still beeping! Can anyone out there enlighten me as to what is going on - can this just be a bad smoke detector or what am I missing? Thanks for any answer!

 

If it is about 10 years old or older, throw it away and get a new one. They're pretty cheap now a days.
You say it beeps when the 120V is off and the battery is removed? How long does it continue beeping, if its more than a few seconds, it might be Possessed, dump it!

 

Put in a fresh, brand new, alkaline 9 volt battery. A "known good" one isn't good enough.

 

What both John and Ron said is accurate. Especially putting in a new battery instead of a known good one. The voltage of a slightly used battery can make the detector react as you discribed.

If you have a battery in that detector and you turn off the power it will beep warning the 120 volts have failed. If you take out the battery and have 120 volts to it then you also will hear it beep until you replace the battery with a new one.

If you have just bought a new smoke detector check to make sure the plastic insulater has been removed from between the battery and the points the battery is supposed to touch. Many people don't realize this plastic insulater is placed to stop the battery from working while they are on the shelf waiting to be sold. You must remove this plastic insulater from new detectors before the battery can work.

One last thought, you may have the red or yellow wire of the detector connecting it to the other detectors as an interconnect. This detector may be beeping because the battery is shot in an interconnected detector remote from that one you are woking on. If you have more than one smoke detector and one battery is worn out. Then you probably would be best off if you replace all the batteries in all the smoke detectors in the house as the same time. This may also be your problem.

Hope this helps

Wg

 

Thanks for the great replies, especially WG. I'm going to get a NEW battery and try it tomorrow; the lady had pulled that battery out of a clock radio she had. One more thing that really mystifies me; after I had unplugged it and removed the battery it still continued to beep - how and where was it getting the power? We had a detector several years ago that did the same thing, and it was still beeping the day I finally tossed it into a dumpster. Any ideas on the Beeping Detectors That Continue To Want Attention?

 

The beeping is telling you that the battery is low and/or the 120-volts are missing. A low battery can still provide enough energy to beep for a long time (which is good). When you think about it, there is nowhere else the power could be coming from.