My neighbors are having a smoke detector problem. It recently started
beeping every 30 seconds or so. The obvious solution is that the beep
is a low battery indication and you should replace the battery, but that
apparently is not the case. The facts as I know them are as follows.
1. The building is a modular home of recent construction with
one floor and a basement.
2. There are a total of 5 smoke detectors. There is one in each
of the bedrooms (3), one in the hallway, and one in the basement.
3. The smoke detectors on the first floor are all BRK 2002RAC. I
forgot to check the model of the one in the basement, but it is
different. I cannot say for sure it is even a BRK unit, but based
on appearance and memory, it was probably BRK 9120B.
4. According to the drawings, the four first floor detectors
were put in by the modular home manufacturer. The one in the
cellar appears to have put by the builder when they were putting
it up. They are all interconnected.
5. The first thing I did was to turn of the breaker (green LED in
unit went out confirming loss of AC) and check the battery in each
of the five units. I replaced four marginal ones. Testing was
done with DVOM and a battery tester that added some load. The
one good battery tested 8.99 V under load. The rest, the were
replaced, were typically 8.5 V. The beeping remained on through
out the process and did not stop even after all units were back in
place with known good batteries and the power restored.
6. The beeps did not always come from the same location, so I
could not tell which unit was the problem one. As a result, I
turned off the AC again, and took all five units down.
7. This is where it gets strange. With all five units out and the
AC power off, the beeps continued from different locations at
different times, and they seemed to be coming from the original
locations in the ceiling, not the units.
8. I then removed the battery from all five units, so none were
powered, just to be sure the units were not beeping. That did not
help as the beeping continued.
I know large value capacitors can can keep things running for a long
time if the load is small, but there were four of us there, including my
wife and the two neighbors, and we all confirmed that the beeping
appeared to be coming from the ceiling mount point, and not the
disconnected units on the floor that had no batteries in them.
Based on this I have a few questions, besides the obvious one of
how to stop the beeping.
1. I realize the smoke detectors are tied together so if one
detects smoke and alarms, they all alarm. Does the same hold true
for the low battery beep, and does it round robin through the
2. Is it possible that there are transducers or other audio
transmitters near the mount point as well as on the unit?
I have never heard of such a thing, but I could see where someone
might of thought it was great idea so that you would still know a
remote sensor was alarming, even if the local unit was completely dead.
The mounting bracket for the detector covered the electrical box
behind it preventing a thorough inspection of what else might might be
in the box besides the wiring.
3. If the sound is coming from the ceiling location, and not the
units themselves, what is the source of the beep and where is the
power for it coming from?
All the units are on the floor, with no batteries in them, and the AC
power has been turned off. The only thing I can think of is that there
is a detector that we have not located that is still connected and it
has a low battery, but if that is the case, it is not shown on the
electrical drawing for the house as constructed, and I can not locate
it. You would think it would not be buried out of sight.
I have looked around the archives for other postings that might be
similar in scope as mine, but could not find any. If I missed one, my
apologies, and please feel free to send me a URL rather than compose a
Thanks for your help,