Repair guide
Carbon monoxide detector beeping
Updated 30 Sep 2026 · AR Logic LLC · 2 sources
Four beeps = emergency
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.
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.
If the alarm is sounding four beeps: do not stop to take a photo. Get out and call 911.
Snap a photo — see what it is, how urgent, who to call.
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Managers: set it up for your buildings →What to check, in order
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].
One chirp about once a minute: battery
Replace the batteries (or the whole unit if it has a sealed battery) [1][2].
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.
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].
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
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.
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.
Sources
Not sure what you’re looking at?
Snap a photo of it. The Triage Profile says what it is, how urgent it is, and who to call.