The Edit — Home Safety
Why a Carbon Monoxide Alarm Chirps, and What to Do
1 chirp a minute is a low battery. A chirp every 30 seconds on a Kidde, or 5 a minute on a First Alert, means the sensor has expired and the alarm must be replaced. 4 beeps and a pause means get out now.
This guide is research-led: we have not handled these units ourselves. If you buy through our links we may earn a commission — it never changes a pick.Research-led, nothing handled. We may earn from links; it never changes a pick. How we choose
This page reads what 2 alarm makers, Kidde and First Alert, publish about their alarms’ sounds, and the CPSC’s carbon monoxide guidance, with 4 replacement alarms chosen as How we choose describes. Nothing here was handled or tested.
Best for An outlet near the bedrooms
Watch for Needs an outlet
Best for Reading the CO level
Watch for Battery changes
Best for A simple spare
Watch for Battery life varies
Best for No battery changes
Watch for Loud warning beeps
4 beeps and a pause means carbon monoxide: get outside
The pattern that matters most is not a chirp. Kidde’s alarm sounds 4 short beeps, then 5 seconds of silence, then repeats. First Alert describes the same thing as 4 beeps and a pause. The CPSC’s advice for suspected carbon monoxide poisoning is to get outside to fresh air immediately, then call 911. Headache, dizziness, weakness, nausea, vomiting, sleepiness and confusion are the symptoms it lists.
Count the chirps to tell a battery from an expired alarm
A chirp is the alarm asking for attention, and the count tells you which kind. Both makers use 1 chirp a minute for a low battery. The expired-sensor signal differs by brand, which is why the count matters.
| What it means | Kidde | First Alert | What to do |
|---|---|---|---|
| Carbon monoxide | 4 short beeps, 5 seconds of silence, repeating | 4 beeps and a pause | Get outside, call 911 |
| Low battery | 1 chirp every 60 seconds | 1 chirp a minute | Change the battery |
| End of life | 1 chirp every 30 seconds | 5 chirps a minute | Replace the alarm |
| Fault | The same 30-second chirp | 3 chirps a minute | Replace it, or call the maker |
A Kidde alarm with a display adds a word: digital models made from February 2006 on show “End” when they expire, Kidde says, and older ones show “Err”.
A chirp every 30 seconds on a Kidde means replace it
Kidde’s guidance is that its alarms chirp every 30 seconds once they reach end of life, 7 or 10 years after first power-up depending on the model, and keep chirping until they are powered off. At that point the alarm can no longer detect carbon monoxide. The same 30-second chirp can also mean a fault, and Kidde’s advice then is to call its support line.
The Kidde plug-in alarm rates 4.8 across 1,308 ratings. Owners call it reliable and simple, value its 10-year life and the AA backup, and say it is worth the price. For a reading on a screen, the Kidde AA alarm shows the CO level and rates 4.7 across 19,928 ratings; owners find it quick to install.
Kidde Carbon Monoxide Detector, Plug-in with AA Battery Backup, 85 dB Alarm
Plugs into a wall outlet, with AA batteries to keep it working when the power goes out.
Current price shown on Amazon. We may earn a commission.
| Power | Plug-in, AA battery backup |
|---|---|
| Alarm | 85 dB |
Owners value the 10-year life and the battery backup. It needs an outlet where the alarm should go.
Buy it if
- Replacing an expired alarm near an outlet by the bedrooms
Don't buy it if
- A hallway with no outlet where the alarm should go
Kidde Carbon Monoxide Detector, AA Battery Powered CO Alarm with LEDs
A battery CO alarm with a display that shows the CO level, on standard AA batteries.
Current price shown on Amazon. We may earn a commission.
| Power | AA batteries |
|---|---|
| Display | CO level |
Owners like the clear CO level display and the standard AA batteries.
Buy it if
- Anyone who wants to read the CO level, not only hear the alarm
Don't buy it if
- A household that forgets battery changes
5 chirps a minute on a First Alert means replace it
First Alert uses 5 chirps a minute for end of life and 3 chirps a minute for a fault, and both mean a new alarm. Its guidance is that most carbon monoxide alarms last 5 to 7 years, and that an alarm should be replaced after 7 years even if its battery is good. Check the date on the back of the alarm: one older than 7 years is due.
The First Alert CO400 rates 4.6 across 22,082 ratings. Owners treat it as an essential alarm, easy to install, and some credit it with saving them. Battery life divides them, with some reporting about 1.5 years.
First Alert Battery Carbon Monoxide Alarm, CO400
A plain battery CO alarm that owners treat as an essential and find easy to install.
Current price shown on Amazon. We may earn a commission.
| Power | Battery |
|---|
Owners call it essential and easy to install. Battery life divides them.
Buy it if
- A spare alarm for a second level or a basement
Don't buy it if
- Anyone who wants a long battery life, which owners split on
A sealed 10-year battery ends the low-battery chirp
An alarm on replaceable batteries chirps each time they run low, which some First Alert CO400 owners report after about 1.5 years. A sealed 10-year battery removes that chirp for the alarm’s whole life, and the alarm is replaced when the battery runs out. The X-Sense SC01 is a smoke and CO alarm on a sealed 10-year battery and rates 4.5 across 2,690 ratings. Owners call it reliable and loud. Some find its warning beeps maddening, and its lifespan divides them.
X-Sense Smoke Detector and Carbon Monoxide Detector, SC01, 1-Pack
One smoke and CO alarm on a sealed 10-year battery, so no low-battery chirp to chase.
Current price shown on Amazon. We may earn a commission.
| Power | Sealed 10-year battery |
|---|---|
| Detects | Smoke and CO |
Owners like the 10-year battery and call it loud. Some find the beeping maddening.
Buy it if
- Ending battery chirps for a decade
Don't buy it if
- Anyone bothered by loud warning beeps
Put an alarm on every level and outside every sleeping area
More than 200 people in the US die every year from accidental non-fire carbon monoxide poisoning linked to consumer products, the CPSC says, and more than 100 of those deaths are linked to portable generators. Its advice is a battery CO alarm, or one with battery backup, on each floor and outside the bedrooms. Interconnected alarms are best, because when one sounds they all sound.
Carbon monoxide detectors compared ranks all 7 alarms, smoke alarms compared covers the ceiling, and the Kidde hardwired profile covers a wired combo for replacing an old ceiling unit.
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