Most carbon monoxide detectors need to be replaced every 5 to 7 years, depending on the manufacturer. The sensor inside gradually loses its ability to detect gas accurately, so even a detector that appears to work fine can become unreliable past its expiration date. Replacing batteries or resetting the unit won’t fix an expired sensor.
Why Detectors Expire
Residential carbon monoxide detectors almost universally use electrochemical sensors. These sensors work by triggering a small chemical reaction when carbon monoxide contacts a liquid electrolyte inside the unit. That reaction produces an electrical signal proportional to the gas concentration, which is how the detector knows when levels are dangerous.
Over time, the electrolyte dries out or degrades. Once that happens, the sensor can no longer react to carbon monoxide reliably. This is a gradual process, not a sudden failure, which makes it especially dangerous. Your detector might still power on, pass a button test, and show a green light while its actual sensitivity to carbon monoxide has dropped well below safe thresholds. That’s why manufacturers set firm expiration dates rather than leaving it to guesswork.
How to Find Your Detector’s Expiration Date
Every carbon monoxide alarm manufactured after August 2009 includes an end-of-life warning. When the unit reaches its expiration, it will chirp in a pattern that differs from a low-battery alert or an actual CO alarm. A single chirp at regular intervals typically means either the battery is low or the detector has reached end of life. If replacing the battery doesn’t stop the chirping, the unit is expired and needs to be replaced entirely.
To check your detector’s age before the chirping starts, remove it from the wall or ceiling and look at the back. You’ll find either a manufacture date or an expiration date printed on a label. If only a manufacture date is listed, add 5 to 7 years (check the manual for your specific model). If you can’t find any date and don’t remember when you bought it, replace it now.
Battery Replacement Schedule
Replacing the detector itself and replacing its batteries are two separate tasks on different timelines. For detectors that use standard batteries (AA or 9-volt), the U.S. Consumer Product Safety Commission recommends swapping in fresh batteries at least once a year. Many people use daylight saving time as a reminder, changing batteries when they adjust their clocks.
Sealed-battery detectors come with a built-in lithium battery designed to last 10 years. These units are meant to be used for their entire lifespan and then discarded as a whole unit. You can’t open them to replace the battery, and you don’t need to. When the sealed battery dies, the detector is likely at or near end of life anyway.
Monthly Testing
The National Fire Protection Association recommends testing your carbon monoxide alarms at least once a month. The test is simple: press and hold the test button on the face of the unit until you hear the alarm sound. This confirms the electronics and horn are working, though it doesn’t test the sensor’s sensitivity to actual gas. Monthly testing catches dead batteries, wiring issues in hardwired units, and outright malfunctions between replacement cycles.
Where Detectors Should Go
Placement matters as much as freshness. The EPA recommends installing a carbon monoxide detector on every floor of your home. If you only have one, put it near the bedrooms and make sure the alarm is loud enough to wake you. Carbon monoxide is slightly lighter than air and mixes evenly throughout a room, so wall-mounted or ceiling-mounted units both work as long as you follow the manufacturer’s specific instructions for distance from corners and vents.
Homes with attached garages, gas furnaces, gas stoves, fireplaces, or any fuel-burning appliances need detectors as a baseline. But CO can also enter from sources you might not expect, like a neighbor’s generator during a power outage or a blocked chimney flue. Having detectors on multiple floors gives you earlier warning regardless of where the gas originates.
Quick Reference
- Full replacement: Every 5 to 7 years (check your model’s expiration date)
- Battery swap: Once a year for standard batteries; not needed for sealed 10-year units
- Button test: Once a month
- Coverage: One detector per floor, prioritizing the area near bedrooms
If your detector is chirping and new batteries don’t stop it, the unit has reached its end of life. At that point, no amount of troubleshooting will restore it. Replace it with a new unit, note the manufacture date, and set a reminder for 5 to 7 years out.