Carbon monoxide alarm beeping? What it means
First, tell the two sounds apart. A loud pattern of beeps, often four quick beeps and a pause, means the alarm has detected carbon monoxide: get everyone outside and call 911 or the fire department from there. A single chirp every minute or so is a low battery or an alarm reaching the end of its life. CO has no smell or color, which is why the alarm is the only warning you get, and why a real alarm always means going outside first and troubleshooting later.
Alarm or chirp?
Carbon monoxide has no smell or color. It can build up from a furnace, water heater, fireplace, gas stove, generator, or a car running in an attached garage. The alarm is the only warning you'll get, which is why an alarm sound always means getting out first, even if everyone feels fine.
CO alarms also wear out. Many are designed to last 5 to 10 years, and they chirp or show a message when the sensor expires. The replace-by date is usually printed on the label.
Why it's beeping
Loud, repeating beeps. Treat it as real every time.
A single chirp about once a minute.
A chirp pattern or screen message that a new battery doesn't stop. The label shows your model's end-of-life signal.
Some models chirp in a different pattern for an internal error. The label or manual says which.
| What you hear | What it usually means | What to do |
|---|---|---|
| Loud beeps in a repeating pattern (often 4 beeps, then a pause) | Carbon monoxide detected | Get outside. Call 911. |
| One short chirp every 30–60 seconds | Low battery | Replace the battery. |
| Chirps with a new battery, or END on the screen | End of life | Replace the alarm. |
| A different chirp pattern | Fault or error | Check the label or manual. |
What to do, step by step
- Listen to the patternLoud, repeating beeps mean CO. Get everyone out, pets too, and call 911 from outside. Don't go back in until responders say it's safe. A single chirp every 30 to 60 seconds is a maintenance signal.
- Check the label or displayTake the alarm down and look at the back. Many list what each sound means and the replace-by date. Some show an error or END message on a small screen.
- Replace the batteryPut in fresh batteries of the type listed. Plug-in and hardwired alarms often have a backup battery too. Some sealed alarms have no battery to change; the whole unit gets replaced.
- Reset and testPut the alarm back, then hold the test button until it sounds. Some models need the button held to clear the chirp after a battery change.
- Replace it if it's expiredIf it's past its date, or still chirps with a fresh battery, replace it. Install the new one following its instructions, and write the install date on it. For a hardwired alarm, switch off its circuit breaker before unplugging the old unit's connector.
Watch it done
- The chirp stops after the battery change and reset
- The alarm sounds when you hold the test button
- The alarm is within its replace-by date
Still chirping with a fresh battery? The alarm needs replacing.
If it keeps chirping
If it still chirps after a new battery, hold the test button to reset it and check the replace-by date. An expired alarm won't stop chirping.
If it's a combination smoke and CO alarm, the manual explains which chirp means what. Our smoke alarm guide covers the smoke side.
What a pro typically charges (a rough estimate; prices vary by area): CO alarms cost about $20–$60. An electrician typically charges $100–$250 to install hardwired alarms, and a heating technician's safety check of a furnace or water heater often runs $100–$250.
Find an electrician near you