Carbon Monoxide Detector Beeping? What Each Pattern Means and What to Do
A CO alarm uses a handful of sounds, and only one of them is an emergency. Knowing which is which lets you act fast on the real thing and fix the rest without guessing.
Quick answer
Four short beeps, a pause, then four more means the alarm has detected carbon monoxide. Get everyone, including pets, outside into fresh air and call 911 from there. A single chirp about once a minute usually means a low battery. A chirp that continues with a fresh battery, often every 30 seconds or in a burst of several beeps, is the end-of-life signal: the sensor has expired and the alarm must be replaced.
- Difficulty
- Easy DIY
- Four beeps, pause, repeating
- CO detected: get out, call 911
- One chirp a minute
- Low battery
- Chirp a new battery won’t stop
- End of life. Replace the alarm
- Replace CO alarms
- At the end of their rated life (often 7 or 10 years)
On this page
Carbon monoxide is a gas you cannot see, smell or taste. It comes from anything that burns fuel: furnaces, water heaters, gas ranges, fireplaces, generators and cars. A CO alarm is the only practical way to know it is there, which is why its emergency pattern deserves an instant response and its maintenance chirps deserve a quick fix rather than a pulled battery.
Four loud beeps, a pause, four more: get out now. Move everyone, including pets, outside or to an open door or window. Call 911 from there. Do not go back inside, or turn the alarm off and ignore it, until responders have checked the air. A digital alarm showing any CO number should be treated the same way, as Kidde advises.
What each sound means
Patterns vary by brand and model. The table shows the two largest brands; your alarm’s exact patterns are printed on its back or in its manual.
| What you hear | First Alert | Kidde | What to do |
|---|---|---|---|
| 4 short beeps, pause, repeating (loud) | Carbon monoxide detected | Carbon monoxide detected | Get out, call 911 |
| 1 chirp about every minute | Low battery | Low battery | Replace the battery |
| Repeating chirps a new battery does not fix | 5 beeps every minute: end of life | A chirp every 30 seconds (with a flashing red light on many models): end of life | Replace the alarm |
| One long, continuous tone | Check manual | Unplugged or loose plug-in alarm, or a malfunction | Reseat it; call the maker if it continues |
| “Lb” or “Err” on a digital display | Check manual | Low battery, or an error code | Replace battery; look up the code |
| Random single beeps | Check manual | Varies; dust, humidity or power blips | Test the alarm; check placement |
If the four-beep alarm sounds
- Get out and get fresh air. Do not stop to look for the source.
- Call 911 or the fire department from outside. Tell them if anyone has symptoms.
- Count heads. Make sure everyone, including anyone asleep, is out.
- Stay out until responders say it is safe. They will measure CO levels and help identify the source.
- Have the source fixed before using the appliance again. A furnace, water heater or other fuel-burning appliance that produced CO needs a qualified technician.
The CDC lists headache, dizziness, weakness, upset stomach, vomiting, chest pain and confusion as the most common symptoms. They are often mistaken for the flu. People who are asleep or have been drinking can die before they notice symptoms.
If it chirps
- Find the chirping alarm.
Stand under each one and wait for the next chirp. Plug-in alarms may be low on an outlet behind furniture.
- Replace the battery.
Use the type printed on the alarm. Plug-in and hardwired CO alarms have backup batteries too.
- Press and hold the test button
until it sounds, then release. This also clears the low-battery memory on many models.
- Check the date if it keeps chirping.
The manufacture or replace-by date is on the back. An alarm at or past its rated life, often 7 or 10 years, is giving its end-of-life warning. Kidde notes a new battery will not stop it, and an expired alarm can no longer detect CO.
- Replace an expired or sealed-battery alarm.
Sealed 10-year alarms cannot take a new battery. When they chirp, the whole unit is due.
Do not silence a chirp by removing the battery and walking away. An alarm with no battery protects no one. If you must take it down, replace it the same day.
Prevent carbon monoxide problems
- Have the furnace, water heater and other fuel-burning appliances serviced by a qualified technician every year, as the CDC recommends.
- Keep vents and flues clear, including outdoor furnace and water heater vents after snowfall.
- Never run a car, generator or other engine in a garage, even with the door open, and never use a grill, camp stove or charcoal indoors.
- Install CO alarms inside bedrooms, outside sleeping areas and on every floor, as NFPA recommends; IBHS also suggests one near an attached garage. Interconnected alarms sound together.
- Test them monthly and replace batteries on the schedule in the manual. First Alert and the CDC suggest every six months for replaceable batteries.
Frequently asked questions
What should I do if my carbon monoxide alarm goes off?
Get everyone outside or to an open door or window, count heads, and call 911 or the fire department. Do not go back in until responders say it is safe. If anyone has a headache, dizziness, nausea, confusion or feels sleepy, tell the dispatcher; carbon monoxide poisoning needs medical care.
Can a carbon monoxide detector go off for no reason?
Alarms can respond to brief sources such as a car warmed up in an attached garage, a blocked flue during a windy day, or a gas range used for a long time with poor ventilation. Treat every alarm as real: get out and call for help. Responders can measure CO and find the source.
Why does my CO detector chirp every 30 seconds?
On many Kidde models, a chirp every 30 seconds is the end-of-life signal, and it continues even with a new battery. First Alert uses five beeps every minute for end of life. Check the manufacture date on the back and the pattern list printed on the alarm or in its manual.
How long do carbon monoxide detectors last?
It depends on the model. Kidde says its CO alarms made since 2013 have a 10-year life; First Alert says most CO alarms last 5 to 7 years, while 10-year sealed models last a decade. The life is printed on the alarm, and it gives an end-of-life signal when the sensor expires.
Where should carbon monoxide detectors go?
According to the IBHS winter checklist, NFPA recommends CO alarms inside every bedroom, outside all sleeping areas, on every floor and wherever local codes require them; IBHS adds one near an attached garage. Follow the placement guidance in the alarm’s manual.
Sources
- Why Is My Carbon Monoxide Alarm Beeping or Chirping? Kidde
- Carbon Monoxide Detector Replacement FAQs Kidde
- Why Is My Carbon Monoxide Detector Beeping? First Alert
- Carbon Monoxide Poisoning Basics Centers for Disease Control and Prevention
- Carbon Monoxide Information Center U.S. Consumer Product Safety Commission
- Winter Ready: How to Protect Your Home From Winter Weather (checklist) Insurance Institute for Business & Home Safety (IBHS)
First published October 7, 2026. Last reviewed October 7, 2026. Spot an error? Tell us and we will check it against the source.