Which smoke detector's battery of 6 is defective?
January 15, 2015 11:36 AM   Subscribe

In my house I have 6 smoke detectors. At least one started going off in the middle of the night to remind me to change the battery. I changed the one I thought was low, and after a repeat performance next night, changed the batteries in all the others. In my house with high ceilings, this is a big deal involving risky ladders in awkward positions. One is still sounding in the night. AARGH! How do I find the one that is still complaining?

In my house with high ceilings, changing smoke detector batteries is a big deal involving risky ladders in awkward positions. A day later after all batteries were changed, one [or more?] sometimes goes off in the daytime too as well as intermittently at night, but I still can't localize the one that is defective. It seems as if one going off triggers all the others, or maybe the sound is so piercing that it just sounds that way. [Bonus question: Is it possibly so, do they listen for each other?] These are 110V hard-wired smoke detectors with a 9-volt battery backup that will chirp intermittently forever if the battery is removed and occasionally scream in the night if the battery is low. How do I isolate and find the defective smoke detector (or more likely, the one with the defective battery)? [Bonus question: Why do they seem always to go off in the middle of the night, and how do they know when to do it?]
posted by SamFrancisco to Home & Garden (16 answers total) 3 users marked this as a favorite
Do you also have any carbon monoxide detectors? They also complain of low battery. I had a beeping noise in my house driving me crazy until I remembered about those.
posted by tomboko at 11:40 AM on January 15, 2015 [2 favorites]

We have two of the hard-wired detectors. One of them died and a replacement battery did not fix it. Both detectors would get triggered. I ended up just throwing the bad detector away (it was a photoelectric model, not the radiation-based or ionization model) and buying another. They were expensive enough ($35) that I didn't want to replace both.

Since you have six, if one of them is faulty and replacement batteries isn't fixing them, you might take down detectors in two batches of three. If the noise continues, the problem is with one of the three you left plugged in. Otherwise, it is a problem with the three you removed. Repeat the test with the problem batch, plugging only two in. If there is no noise, the bad detector is the one in your hand. Otherwise, remove one more detector. If there is no noise, the detector is the one in your hand.
posted by a lungful of dragon at 11:47 AM on January 15, 2015 [1 favorite]

Best answer: Smoke detectors chirp for several reasons. And I know it can be annoying. the chirping is meant to be annoying, so that you can not ignore it.

Besides the battery being replaced, other reasons include: a) There might be a short in the circuit, and if the detector is not getting proper primary power, it will chirp. b) sometimes you need to re-set the detector after replacing a battery (hold the test button for 15 seconds). c) connections might have dust in them, making a bad connection. d) smoke detectors have a life span of 10 years. NFPA code says to replace with new detector every 10 years. if the detector fails, it might chirp until replaced with a new one.

I am an electrical contractor. I have trouble-shot this issue for customers. I can tell you, it can sometimes be a huge pain in the butt trying to figure out exactly why these things are chirping.
posted by Flood at 11:49 AM on January 15, 2015 [3 favorites]

Best answer: Recent Building Code here in North Carolina requires the "interconnectedness" you refer to. If one goes off some kind of central system has to "notify" the whole building. In the case of my home this is accomplished by the smoke detectors being part of the security system. If one goes off the nice robot voice announces this through speakers on each floor. Same thing for low batteries. Thankfully each detector has a specific number so the announcement says "Low battery in detector x" and I have a list which is which.

Sorry but this probably doesn't directly help you.
posted by achrise at 11:51 AM on January 15, 2015

They could be interconnected, either wired or wireless. There should be some indicator of which one has alarmed.
posted by H21 at 11:52 AM on January 15, 2015

Best answer: Unfortunately, I'd say you need to get back up on the ladders and double check the battery connections on all 6.

Why do they seem always to go off in the middle of the night, and how do they know when to do it?

I don't know if this is really true but an electrical engineer friend once said it was due to the drop in house temperatures at night that caused very slight voltage drops in small batteries, which is why it's always like 2 or 3 in the morning when they chirp because that's the coldest part of the night.
posted by mathowie at 11:54 AM on January 15, 2015 [4 favorites]

I'd have the ladder, batteries, flashlights ready to go and actually get up when it starts alarming in the middle of the night so you can check them when its happening. I haven't figured out a better way. they usually stop by the time its a reasonable hour.

Where i rent one of the smoke detectors was doing the same thing around 4am on the weekends sometimes, but would stop by the time i got out of bed at a reasonable hour. I finally got fed up and was running around in my robe so i could finally figure out which was the offender.
posted by TheAdamist at 11:58 AM on January 15, 2015

Also, while you're up there, take a handheld vacuum, if you have one, and vacuum them out. We had what we thought was a battery situation like yours, that turned out to be a (small) spider situation.
posted by gingerbeer at 12:19 PM on January 15, 2015 [1 favorite]

Yeah, this happened to me, and it was the carbon monoxide detector. D'oh. Try that! Alternately, I wonder if a decibel meter on your phone could help pinpoint the source if your ears are unable?
posted by acidic at 1:05 PM on January 15, 2015

There is often a detector near the furnace. We did not know this, and could not find the beeping until someone tipped us off to this phenomenon. Sure enough, the beeping smoke detector was in the basement on a wall near the furnace, behind some cobwebs.
posted by vitabellosi at 1:10 PM on January 15, 2015

Ugh, I feel your pain. Been there, done this. What finally solved it for us was painstakingly changing all of the batteries in each of the many detectors high up there, and making sure all of the batteries were installed properly (for real), and that all of the dust and dead bugs that had collected in the little crevices in there were all cleaned out first.
posted by hush at 2:16 PM on January 15, 2015

seconding the age thing. this stirred up some old ass discarded memory, but when i lived with my parents in the building they managed random weird issues like this led to EVERY smoke detector being replaced. it wasn't the batteries, the old ones(from the late 80s/early 90s, in the early 2000s, so basically 10 years old) had just gone wrong some how. photocell filled with dirt that couldn't be cleaned? electrical fault? who knows. i dissected one and it looked fine, but they just started intermittently being insufferable.

if they're from well, the early 2000s, it might be new detector time again.

as another random data point, my current building seems to have put in all new detectors around 2012-2013. i can't verify that the old ones were replaced around the same time, but i'm wondering if there's some real meat to the 10 year thing. maybe the swaps happened around the same time because they were mandated the same year, and have been getting swapped about every 10 years since then? That was my dumb theory at least.

there's absolutely something to the age thing though.
posted by emptythought at 4:42 AM on January 16, 2015

Detectors certainly expire as they contain small amounts of radioactive material and those decay and become in effective.
posted by Mitheral at 9:32 AM on January 16, 2015

Detectors certainly expire as they contain small amounts of radioactive material and those decay and become in effective.

The half-life of the radioactive material in ionization smoke alarms is ~430 years. It is more likely the electronics will fail many hundreds of years before the ionization source decays to the extent its emissions are undetectable — after an ionization smoke detector's projected 10-year lifespan, the amount of radioactive material (and therefore its activity) is almost the same.
posted by a lungful of dragon at 12:34 PM on January 16, 2015

Geez, so it is and I suppose a minute's critical thinking should have at least made me wonder. My bad. At any rate they do wear out even if the mechanism isn't lack of radioactivity. I've replaced hundreds of expired detectors when they've started acting up.
posted by Mitheral at 4:17 PM on January 16, 2015

Best answer: By sheer luck, it went off in the daytime and I was able to localize it by the sound, replace one battery (by good fortune, the easiest one to reach), and now regard the problem as solved. Just wait another 6 months! :-) Thanks for your support, hive mind!
posted by SamFrancisco at 11:35 AM on January 18, 2015

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