Important: if your carbon monoxide (CO) alarm is sounding a loud, repeating alarm, treat it as a real emergency. Get everyone, including pets, outside into fresh air right away, and call your local emergency number from outside. Don’t go back in until emergency services say it’s safe.
Carbon monoxide has no smell, taste or color, so you can’t tell whether it’s there. That’s why a carbon monoxide detector beeping should never be ignored. Many of the sounds a CO alarm makes are just maintenance warnings, though, like a low battery. This guide explains how to tell the difference.
Quick answer: on many CO alarms, 4 loud beeps, a pause, then repeat means carbon monoxide has been detected, so get out. One short chirp about every minute usually means a low battery. Five chirps about every minute on many models means the alarm has reached the end of its life and must be replaced. Patterns vary by brand, so check the label on the back of your alarm.
What the beeps usually mean
- 4 beeps, pause, repeat (loud): CO emergency on many alarms. Get outside and call for help.
- 1 chirp every minute or so: low battery on many alarms.
- 5 chirps every minute or so: end of life on many models. The whole alarm needs replacing.
- Other chirp patterns or a flashing light: often a fault or error. Check the back of the alarm or the manual.
- Voice messages: some alarms say “Warning: carbon monoxide” or “Low battery”. Follow what it says.
Combination smoke and CO alarms use different sounds for smoke and for carbon monoxide. For smoke alarm sounds, see our guide on why your smoke detector is beeping.
If the alarm is going off: what to do
- Get everyone outside into fresh air immediately.
- Call your local emergency number from outside the home.
- Don’t go back inside until emergency responders tell you it’s safe.
- Watch for symptoms of CO poisoning, which can feel like the flu: headache, dizziness, weakness, nausea or confusion. Anyone with symptoms needs medical help right away.
After the emergency, have a qualified technician check fuel-burning appliances such as the furnace, water heater, gas stove and fireplace, which are common sources of carbon monoxide.
1. Low-battery chirp
A single chirp every minute or so is the most common sound, and it usually means the battery is low. Replace it with the type shown on the alarm. Some newer alarms have a sealed battery that lasts the life of the alarm, so the whole unit has to be replaced instead.
2. Still chirping after a new battery
- Make sure the battery is the right type and fully seated, with the contacts touching.
- Close the battery door completely. Some alarms won’t work properly until it clicks shut.
- Press and hold the Test or Reset button for a few seconds after changing the battery.
- Use a fresh battery from a new pack, not an old one from a drawer.
💡 Tip: Write the installation date on the back of every new CO alarm with a marker. When it starts chirping years later, you’ll know straight away whether it’s a battery issue or the alarm has reached the end of its life.
3. End-of-life warning
CO alarms don’t last forever. The sensor wears out over time, and many alarms need replacing somewhere between 5 and 10 years after they were made, depending on the model. Many models give a special chirp pattern, often 5 chirps a minute, when they reach that point. A new battery won’t stop it. Check the date on the back and replace the alarm.
4. Fault or error chirps
If the pattern doesn’t match a low battery or end of life, the alarm may have a fault. Press Test or Reset, and check the manual or the label on the back for that pattern. If the fault doesn’t clear, replace the alarm, because a faulty CO alarm may not warn you when it needs to.
Where CO alarms should be
- Outside each sleeping area, so you’ll hear them at night.
- On every level of the home, including the basement.
- Following the manufacturer’s instructions for height and distance from fuel-burning appliances.
The NFPA’s carbon monoxide safety page has more advice on where to put alarms and how to test them.
Carbon monoxide detector beeping: quick FAQ
Why is my carbon monoxide detector beeping 4 times?
On many alarms, 4 beeps in a repeating pattern is the CO alarm signal. Treat it as an emergency, get outside, and call for help.
Why is my CO detector chirping every minute?
Usually a low battery. If it continues with a new battery, try resetting it, and check whether it has reached its end-of-life date.
Can I just take the battery out to stop the chirping?
Please don’t. Without power, the alarm can’t warn you about carbon monoxide. Replace the battery or the alarm as soon as possible.
Related guides: Why Is My Smoke Detector Beeping? · Water Heater Leaking From the Bottom?