A smoke and CO alarm on a dark ceiling, its light glowing
FOUR BEEPS = EMERGENCY

Carbon monoxide detector beeping

Four beeps means get out. A single chirp is usually the battery. Know which one you’re hearing.

If the alarm is sounding four beeps: do not stop to take a photo. Get out and call 911.

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Updated 30 Sep 2026 · AR Logic LLC · 2 sources

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Is a beeping carbon monoxide detector an emergency?

The alarm pattern is — four beeps, a pause, four beeps: get everyone out to fresh air, call 911 from outside, and do not go back in until the fire department says it is safe. A single chirp every minute or so is a battery or end-of-life warning, not an alarm, but it means the detector may not protect you: fix it today.

Four loud beeps, a pause, and four again is the alarm: carbon monoxide has been detected, so get everyone outside into fresh air and call 911. A single short chirp about once a minute is usually a low battery, and a chirp every 30 seconds or five chirps a minute usually means the alarm has reached the end of its life and must be replaced.

Everything else about a beeping CO detector

What to check, in order
  1. 1

    Four beeps, pause, four beeps: get out

    This is the carbon monoxide alarm on First Alert and Kidde alarms and most others [1][2]. Leave, call 911 from outside, and do not assume it is false. Headache, dizziness, nausea and confusion are symptoms of CO poisoning [1].

  2. 2

    One chirp about once a minute: battery

    Replace the batteries (or the whole unit if it has a sealed battery) [1][2].

  3. 3

    Five chirps a minute, or a chirp every 30 seconds: end of life

    First Alert uses five chirps a minute; a Kidde alarm chirps every 30 seconds starting seven years after it was first powered, and it will not detect CO in that state [1][2]. Replace the alarm — the sensor, not the battery, has worn out.

  4. 4

    A display that says ERR or END

    Look the code up in the manual printed on the back of the alarm or on the maker’s site [2].

  5. 5

    After an alarm: find the source

    Carbon monoxide comes from things that burn fuel — a furnace, a gas water heater, a gas range or dryer, a fireplace, a car or generator in or near the house. Have a qualified technician check every fuel-burning appliance before using them again.

By brand
First Alert
4 beeps and a pause = CO; 1 beep a minute = low battery; 5 beeps a minute = end of life [1].
Kidde
4 short beeps, 5 seconds of silence, repeated = CO; 1 chirp every 60 seconds = low battery; 1 chirp every 30 seconds = end of life (7 years after first power-up) or a fault [2].
Safety first
  • Never silence a CO alarm and stay inside to “see if it stops”.
  • Never run a generator, grill or car in a garage or near windows; never heat a home with a gas oven.
  • Test alarms monthly with the test button.
When to call a pro

After any alarm: the fire department first, then a licensed HVAC technician or plumber to inspect the fuel-burning appliances. For a chirping unit, no pro is needed — replace the battery or the alarm.

What to photograph

For the Triage Profile, photograph the back of the alarm, with the manufacture date and model visible — not needed if it is sounding the four-beep alarm: leave instead. One clear photo in good light is enough; the Triage Profile says what it is, how urgent it is (emergency, today, this week or whenever), and which trade to call.

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Questions people ask

How long do carbon monoxide detectors last?

Most last five to seven years; ten-year sealed-battery models last about ten. The date is printed on the back [1].

It stopped beeping when I opened a window. Am I safe?

Not necessarily — fresh air lowers the level but the source is still there. Stay out and call 911.

Related problems

Related guides

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Sources
  1. First Alert — What does the beep mean?
  2. Kidde — Why is my carbon monoxide alarm beeping or chirping?

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