When should I replace a carbon monoxide detector?

Short answer

Replace your carbon monoxide detector every 5–7 years. The electrochemical sensor inside degrades over time and stops detecting CO accurately — even if the unit still beeps and appears to work. Check the manufacture date on the back of the unit.

Why detectors expire

CO detectors use an electrochemical sensor that reacts with carbon monoxide. Over 5–7 years, the chemicals in this sensor degrade and lose sensitivity. The unit may still chirp for low battery or pass a test button press — but it may no longer detect real CO levels accurately.

This is different from smoke detectors, which last 8–10 years.

How to find the manufacture date

Flip the detector over or remove it from the wall
Look for a label with a manufacture or "replace by" date
If you can't find a date, it's likely old enough to replace

Most manufacturers print the date on the back. If yours doesn't have one, replace it.

Signs it needs immediate replacement

Chirping repeatedly (not the low battery chirp — a different pattern)
End-of-life alarm: many detectors beep 4 times, pause, repeat when they've expired
7+ years old — replace regardless of apparent function
After a CO event — sensors can be damaged by high CO exposure

Best CO detectors to buy

Kidde Nighthawk (~$30) — reliable, plug-in with battery backup
First Alert CO400 (~$20) — battery powered, simple
Nest Protect (~$119) — smoke + CO combo, smart alerts to phone

Where to place CO detectors

On every floor of your home
Near sleeping areas (CO is most dangerous at night)
Near attached garage (car exhaust)
Not directly next to a gas stove or fireplace (causes false alarms)

Common mistakes

Assuming the test button proves the sensor works — it only tests the alarm circuit, not the sensor
Only having one detector in the whole house
Placing it too close to a fuel-burning appliance