Carbon monoxide detector beeping: what it means and what to do

Treat every carbon monoxide alarm as real: get everyone outside first, then call 911.

Area: SafetyFrom age 12Time to learn: 20 minutes, plus 1 minute a month to testPractise in a class

Put a carbon monoxide (CO) alarm in and near every place people sleep and on every level of your home. Learn to tell the danger pattern from the maintenance chirps. When the danger pattern sounds, get everyone outside and call 911.

SafetyIf a CO alarm sounds, or anyone has a headache, dizziness, weakness, an upset stomach, vomiting, chest pain or confusion that could be from carbon monoxide, go outside right away and call 911. Never run a car, generator or grill inside a home or garage, even with the door open. Check your alarm's manual for its exact signals.

Why it matters

Carbon monoxide is a colorless gas with no smell, so the alarm is the only warning you are likely to get. Early symptoms such as headache, dizziness and an upset stomach feel like the flu, and people who are asleep can die before they notice anything. CO alarms make a loud pattern for danger and quieter chirps for low batteries and end of life. Confusing the two can lead someone to silence a real alarm and go back to bed.

Each year, more than 400 Americans die from unintentional carbon monoxide poisoning not linked to fires, more than 100,000 visit an emergency department and more than 14,000 are hospitalized.

Source: US Centers for Disease Control and Prevention: About Carbon Monoxide Poisoning, 2026.Measured

How to do it

Place CO alarms in every room where someone sleeps, outside each separate sleeping area, and on every level of the home, including the basement. Mount each alarm where its manual says. A combination smoke and CO alarm goes where a smoke alarm would go.
Buy alarms listed by a recognized testing laboratory. Interconnect them if you can, so that when one sounds, they all sound.
Press the test button on every alarm once a month.
Learn the danger signal. On most alarms it is 4 short beeps, about 5 seconds of silence, then 4 beeps again, repeating. If your alarm has a digital display, check its manual for what a normal reading looks like. Kidde advises treating any CO number on its displays as CO present, even if the alarm is not sounding.
When the danger signal sounds, go outside immediately and take everyone with you, pets included. Do not stay behind to look for the source.
Once you are outside, call 911. Stay outside until emergency responders tell you it is safe to go back in.
Learn the low-battery chirp: 1 chirp about every minute. Replace the batteries. If the alarm still sounds after that, treat it as the danger signal: go to fresh air and call 911.
Learn your brand's end-of-life signal, which means the sensor has stopped working. Kidde alarms chirp every 30 seconds at end of life, which on many models begins 7 years after they are first powered up. First Alert alarms give 5 chirps every minute. Replace the whole alarm, not just the battery.
Replace each alarm by the date the manufacturer gives. If you cannot find a date and the alarm was installed 5 or more years ago, replace it. Write the installation date on the back of each new alarm.

Common mistakes

Pressing silence and going back to sleep because nobody feels ill. People who are asleep can die before they notice any symptoms.
Expecting to smell a leak. Carbon monoxide has no smell, so what you can smell from a furnace or a car is other exhaust, not CO.
Changing the battery when the end-of-life signal sounds. The sensor is worn out and the whole alarm has to be replaced.
Relying on smoke alarms. A smoke alarm does not detect carbon monoxide unless it is a combination unit, and a CO alarm does not replace a smoke alarm.

You can do this when …every sleeping area and every level of your home has a working CO alarm, you can tell the 4-beep danger signal from a low-battery chirp, and everyone in your household knows to go outside and call 911 from there.

Reading is not training. Practise on a manikin or in a supervised class with the American Red Cross or the American Heart Association, or in Canada with the Heart and Stroke Foundation, St John Ambulance or the Canadian Red Cross.