Vent, Valve & Volt
Carbon monoxide alarm going off or beeping

You can fix this

Likely cause: a low battery

If anyone feels unwell or the alarm sounds more than one beep in a row, get everyone outside and call 911. Kidde says one chirp about every minute may mean a low battery, and First Alert lists one beep every minute as low battery. Your manual has the final word for your model. Replace the battery the way your manual shows. If yours is hardwired, this one is for a licensed electrician.

Why this happens

Kidde says a CO alarm that chirps once every 60 seconds may have a low battery, and First Alert lists one beep every minute as low battery. Kidde adds that digital models show Lb for a low battery. NFPA says that if the audible low-battery signal sounds you should replace the batteries or the device, and that if the CO alarm still sounds you should get to fresh air and call 911.

How to fix it

  1. Make sure nobody feels unwell and that this is a chirp, not the loud four-beep alarm. If anyone feels unwell or the loud alarm sounds, leave and call 911.
  2. If your alarm is hardwired, stop here. Do not take it off its mounting plate or disconnect its wiring. Call a licensed electrician to change the backup battery.
  3. Find the battery type and the replacement steps in your alarm's manual. Kidde says its models differ, to use the same type of battery, and to follow the manual.
  4. Some alarms have a sealed battery. First Alert says its 10-year sealed batteries last the life of the alarm. If your manual shows a sealed battery, there is no battery to swap, so replace the alarm instead.
  5. If it plugs into an outlet, follow the manual for the backup battery, and stop if the manual has you open anything other than a battery door.
  6. Kidde recommends changing alarm batteries every six months, such as when the clocks change, and NFPA says to test CO alarms at least once a month.
  7. NFPA says that if the CO alarm still sounds after you replace the batteries or the device, get to fresh air and call 911. Kidde says new batteries will not stop an end-of-life chirp, so do not keep swapping batteries.

When to stop. If anyone feels unwell or the loud alarm sounds, get everyone outside, pets included, and call 911 from outside. That is an emergency.

If this does not fix it, tell the HVAC technician

  • If it keeps chirping: the alarm's brand, model and the label date.
  • How often it chirps and whether the display shows Lb, End or an error.
  • Whether the alarm is battery-only, plug-in or hardwired.

Build the full list: what to tell the HVAC technician.

Related troubleshooters

Start this troubleshooter over

References (every fact above comes from one of these pages)
  1. Kidde: Why is my carbon monoxide alarm beeping or chirping?
  2. Kidde: Carbon monoxide or combination alarm battery replacement
  3. First Alert: Why is my carbon monoxide detector beeping?
  4. NFPA: Educational messages desk reference, chapter 3, carbon monoxide (PDF)
  5. Kidde: Carbon monoxide detector replacement FAQs

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