My 2-years old CO detector (small, wall-mounted device with battery, no other power source) started beeping every morning for at least few minutes, sending sharp chirps once every 10 sec. It starts around 6am.

I don't see any visible fire or cooking in my apartment or outside. I've read that it might mean end of battery/detector life, temperature change, or poltergeist. Are these the most common reasons?

I will replace battery to check for some of it.

UPDATE: Changed battery, chirping went away

  • 26
    Just FYI, a CO detector detects a deadly invisible odorless gas. If it starts blaring the full alarm (whatever it sounds like when you push the test button), leave the building immediately and call 911 or your country-specific emergency number. Do not check for fire, cooking, or other causes.
    – MooseBoys
    Commented Jul 13, 2018 at 16:55
  • 4
    If a new battery doesn't fix it, call the manufacturer. I had a CO detector that started chirping when it was a couple years old, and they sent me a free replacement because they determined it was defective.
    – mrog
    Commented Jul 13, 2018 at 21:12
  • Does the detector have a display that can show you the maximum CO level detected? If so, reset the max value, then wait a day and check it again. If it's much above 0, you might need to start investigating. Start with things that might see more use around 6 AM, such as a water heater. Your gas company (if you have one) may be willing to check CO levels around the house for free.
    – mrog
    Commented Jul 13, 2018 at 21:19
  • 4
    I take it the sun does not shine in the window on the device at 6 am?
    – Willtech
    Commented Jul 14, 2018 at 3:54
  • @Willtech no :) Commented Jul 14, 2018 at 20:58

5 Answers 5


If your CO detector were actually detecting CO, it would not chirp. It would sound a continuous, and very, VERY loud alarm you would definitely recognize.

The chirping is a universal (as far as I know) method for indicating that it's time to change the battery. This is true for CO and smoke detectors.

  • 21
    +1 It's very hard to miss an active alarm
    – mmathis
    Commented Jul 13, 2018 at 13:48
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    @Harper In which case wouldn't it block actual smoke from getting to the detector to be detected? Commented Jul 14, 2018 at 18:42
  • 1
    Yes, covering a detector with an impermeable substance is life endingly dangerous. Commented Jul 16, 2018 at 11:58
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    @CarlWitthoft be convinced: batteryuniversity.com/index.php/learn/article/… Commented Jul 16, 2018 at 14:35
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    To spell it out more clearly. Temp gets colder, battery which is starting to near end of life produces less voltage because chemistry. Detector detects this, chirps. Temp warms up. Battery warms up. Chemistry causes more voltage and detector thinks battery is now fine. Commented Jul 16, 2018 at 14:54

It's normal for gas and smoke detector batteries to indicate impending failure during the coolest part of the day. The chemical reaction that produces the electrical current is reduced by low temperatures. It's a common occurrence in cold climates, especially in the case of vacation homes that are kept at lower temperatures when not in use.

Chances are the battery should've been replaced long ago. Do it now and see what happens.

  • I am in LA and run AC overnight Commented Jul 13, 2018 at 14:59
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    6 AM is generally the coldest part of the day, just before local dawn.
    – Criggie
    Commented Jul 13, 2018 at 21:15
  • FWIW, the coldest part of the day is normall after dawn. :)
    – isherwood
    Commented Jul 16, 2018 at 18:34

A low battery is the most common cause of seemingly-random chirps in smoke and CO detectors. Detector end of life is probably the second most common cause.

How old is the CO detector? Their lifetime is somewhere in the range of 5-10 years, depending on the make/model (source source source), so if it that old or older, it's best to replace the whole thing.

  • The claim that it should be replaced is one strong enough that I'd like to see some supporting source material for it. (I know it's correct, i'm just saying we should source it) Commented Jul 13, 2018 at 13:38
  • CO sensors can last less than 10 yrs, especially if there are low levels of CO. It's usually a chemical-based sensor and it can handle a certain total amount of CO. That can be a few events with enough to trigger the alarm, or a small amount over a long period.
    – fixer1234
    Commented Jul 13, 2018 at 13:42
  • 1
    @TheEvilGreebo Added links. Some only last 5-7 years
    – mmathis
    Commented Jul 13, 2018 at 13:44
  • I wouldn't call it "seemingly-random" because it started at 5:30-6:20 every time. But point taken. CO detector is like 2 years old Commented Jul 13, 2018 at 14:58
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    Is 5:30 when your house reaches its lowest temperature? The battery may be teetering around whatever voltage level triggers the beeping, dropping below the beep threshold when it is coldest and then rising just marginally (enough for the beeping to stop) as it warms up during the day.
    – CactusCake
    Commented Jul 13, 2018 at 15:44

Volunteer firefighter here who has seen many a CO detector malfunction..

I think the answers here are spot on but I'll just add on:

  1. Some CO detectors, when set off, sounds like a BEEP-BEEP-BEEP then a pause and it continues with the series of beeps, etc. They're loud but not as loud as a commercial fire alarm in say a school or public building is. Most detectors go off at the early stages of CO being a problem (10-15ppm). As firefighters we have to put on our SCBA (masks) at 70ppm (this varies by department)

  2. Definitely check the back of your detector and look for the date of manufacture. If it was manufactured 4-5 years ago it may be time to get a new one. CO detectors don't last forever so replace it if it's old.

  3. And of course, make sure you replace the batteries, or at least check them, every 6 months or so. The cold causing he low power alert to go off is plausible but if it continues you may have to replace it (see above!) Some detectors plug right into the wall but have battery backups. Make sure you still check those as well!

  4. Of course, if it ever does go off, do not hesitate to call 911. The fire department has the tools to check your home if it is hazardous to your health. A CO alarm is definitely no laughing matter and it should be taken seriously.

  • A CO detector should be BEEP-BEEP-BEEP-BEEP-pause (Temporal-Four) -- BEEP-BEEP-BEEP-pause (Temporal-Three) is reserved for fire or smoke alarms. (Good to know, especially if you have combo smoke/CO alarms) Commented Jul 16, 2018 at 4:39

If the battery were failing, it would not chirp at the same time every day, it would chirp and continue chirping all day. Having said that, if it's easy, and it should be, replace the battery. If it still chirps - at the same time every day- you can rule out battery. this is the first step.

The next step is to look outside at the neighbor's car.

  • Good point about the time of day. I read about one CO alarm that would chirp for very low levels of CO. Apparently, it wouldn't switch to a continuous alarm until the CO level reached a higher threshold. It could be that some CO source (car, water heater, etc.) starts working around 6 am and triggers the detector just barely.
    – mrog
    Commented Jul 13, 2018 at 21:17
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    Good point about the time of day. Usually, 6 am is around the coldest point of the day, a time at which most standard day-to-day batteries are least efficient.
    – Willtech
    Commented Jul 14, 2018 at 3:54
  • This is incorrect. In northern climates it's very common for detectors to chirp low battery warnings at night (or when away from a vacation home with the heat turned down) and not during the times when the furnace is set to a warmer temperature. Most, in my experience, don't have the "intelligence" to store a low battery warning and reset it when the battery is changed. It's a continuous voltage monitor and that's it.
    – isherwood
    Commented Jul 16, 2018 at 13:48

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