Test a carbon monoxide (CO) alarm once a month with its test button and replace the batteries once a year, which is what the US Consumer Product Safety Commission recommends. Replace the whole alarm by the date on its label. For most current models that's 7 to 10 years after manufacture, and a new battery doesn't extend it.
If your CO alarm is going off right now#
Get everyone, including pets, outside into fresh air. Then call 911 or your local emergency number from outside. Don't hunt for the source first, and don't go back in until the fire department or gas company says it's safe.
That's the CPSC's advice for a sounding CO alarm, and it applies even if nobody feels ill. Early CO poisoning feels like flu without the fever: headache, tiredness, shortness of breath, nausea, dizziness. If the alarm goes off again within a day of returning, the CPSC says to get out again and have a qualified technician check every fuel-burning appliance.
How to test a carbon monoxide alarm#
- Warn the household. The test tone is loud, and on a combination alarm it may sound like the smoke alarm.
- Press and hold the test button for as long as the manual says. Some alarms need a few seconds, and some voice models announce "carbon monoxide" or "fire" so you can tell the patterns apart.
- Check the power light. A plug-in or hardwired alarm still needs its backup battery, and a dead backup won't help you in a power cut, which is exactly when people run generators and gas heaters.
- Read the replace-by date on the label while you're there. Photograph it once so you don't have to unplug or unscrew the alarm next time.
The test button has a limit worth knowing. The CPSC points out that it checks whether the circuitry works, not how accurate the sensor is. That's why the replacement date matters as much as the monthly test: an old sensor can pass the button test and still be past its working life.
Don't test a CO alarm with car exhaust or a smoldering anything. The button is the test.
How long do carbon monoxide detectors last?#
Usually 7 to 10 years, and the label on the back is the final word. Kidde says its CO alarms last seven to ten years depending on the model. Its alarms made since 2013 mostly have a 10-year life, and those made before 2013 have a seven-year life. Other brands print their own dates.
If your alarm is a combination smoke and CO unit, the CO side sets the deadline. Replace it when the CO sensor expires, even if a smoke-only alarm of the same age would have a few years left.
Most current alarms announce their end of life with a chirp or light pattern that new batteries won't fix.
What do the chirps mean?#
Patterns vary by brand and model, so look yours up. As one example, Kidde describes these patterns for its combination alarms:
| What you hear |
What it usually means |
What to do |
| A chirp every 60 seconds |
Battery too low to run a full alarm |
Fit a fresh battery |
| A chirp every 30 seconds |
End of life or a sensor error |
Replace the alarm |
| Chirping that continues after a new battery |
End of life or a fault |
Replace the alarm |
An end-of-life or sensor-error signal won't respond to a battery change. Treat a unit that does this as already dead, and fit the new one the same day.
Where to put CO alarms#
The CPSC recommends a CO alarm on every level of the home and outside each sleeping area. Avoid spots near heating vents or behind curtains and furniture. The CPSC also advises against putting them in kitchens or right above fuel-burning appliances, and against attics and basements unless someone sleeps there.
According to the CPSC, a CO alarm can plug into a wall outlet or mount high on a wall. Your manual sets the exact position, so check it instead of copying where the smoke alarm went.
Cutting the risk in the first place#
An alarm is a backstop. The CPSC lists faulty furnaces, ranges, water heaters and room heaters as common sources, and recommends having the heating system professionally inspected and serviced every year. A few hard rules from the same guidance:
- Never run a portable generator or any gasoline engine in or near an enclosed space. Open doors and windows don't make it safe.
- Never leave a car running in an attached garage, even with the garage door open.
- Never burn charcoal inside a home, garage, vehicle or tent.
If you burn wood or gas through a flue, add a yearly chimney inspection to the list, and keep your water heater on its service schedule.
A simple schedule#
Test monthly. Change replaceable batteries once a year. Replace the alarm by its label date. Set the monthly test as a repeating reminder in ChoreLists.com and put each alarm's replace-by year in its own reminder so it doesn't depend on someone remembering. The test fits neatly into the same round as your smoke alarm check.