How long does a carbon monoxide detector last?
Updated August 2026
A carbon monoxide detector lasts 5 to 7 years, noticeably shorter than a smoke alarm, because its gas sensor has a fixed chemical life. The electrochemical cell inside slowly exhausts itself whether or not any CO is ever present, and once it is spent the unit can still power on, light up, and even chirp while no longer able to sense the gas at all. Newer models are rated to 7 or 10 years and many now flash an end-of-life warning near the date they expire. A working alarm is calibrated to sound at sustained low levels, around 70 ppm, well before the gas turns deadly. Since carbon monoxide is invisible and odorless, a dead detector is worse than none, because it hands you false confidence. Units cost $20–60.
Lifespan by type and situation
| Type or situation | Typical lifespan | Why |
|---|---|---|
| Standard CO alarm | 5–7 years | The electrochemical sensor sets the limit, not the battery |
| Newer 7-to-10-year model | 7–10 years | Longer-life sensor; check the printed end-of-life date |
| Combination smoke and CO alarm | 7–10 years | Matches the shorter-lived CO half |
| Sealed 10-year battery unit | 7–10 years | Battery and sensor timed to end together |
| 9-volt battery | About 1 year | Chirps when low; swap yearly, test monthly |
Signs yours is near the end
- A printed manufacture or "replace by" date that has arrived or passed
- An end-of-life signal: a distinct chirp pattern that returns even on a fresh battery
- No reading or a stuck display on a digital model
- Failure to respond to a canned-CO test spray while the test button still beeps
- A unit with no date on it at all, a sign it predates current labeling
- Yellowed housing on a plug-in that has baked in an outlet for years
How to add years
You cannot refill a CO sensor, so the job is making sure a live one is always on the wall. Test each alarm monthly with the button, and replace the 9-volt battery once a year. Learn your model's end-of-life chirp, and do not silence it for weeks, since that specific pattern often means the sensor is done. At the 5-to-7-year mark, replace the whole unit, and put one on every level and near every sleeping area. Skipping CO protection is a gamble with a gas you cannot see or smell.
What it costs to replace: plan on $20–60 per unit ($40–80 for a combination smoke and CO alarm). Replacing on your own schedule, before it fails, is almost always cheaper than the emergency version. The home maintenance cost calculator helps you set the money aside before it comes due.
OnOtto tracks your CO detector tests age and service history, and warns you before end of life instead of after the flood.
Track your home's systems, free for 30 daysFrequently asked questions
Why does a carbon monoxide detector expire faster than a smoke alarm?
Different sensor, different clock. A smoke alarm reads particles in the air with a sensor good for about 10 years. A CO alarm uses an electrochemical cell that reacts with the gas, and that cell slowly wears out on its own, typically in 5 to 7 years, whether or not it ever meets any carbon monoxide. Newer designs stretch that to 7 or 10 years, but the sensor, not the battery or the housing, is always the limiting part. When the date is up, the whole unit goes.
My carbon monoxide detector keeps chirping but there is no gas. Why?
Two common causes, and they sound different. A single chirp every 30 to 60 seconds usually means a low battery, fixed with a fresh 9-volt. A different pattern, often five beeps or a repeating chirp that a new battery does not silence, is the end-of-life signal telling you the sensor has expired. Check the date on the back: if it is 5 to 7 years old, replace it. If the alarm is instead sounding a full, continuous pattern, treat it as real, get everyone outside, and call 911.
Where should I put carbon monoxide detectors?
One on every level of the home and one within about 10 feet of each sleeping area, so a night-time leak wakes you. Keep them at least 15 feet from fuel-burning appliances like the furnace, water heater, or stove to avoid nuisance trips from brief startup spikes. Height is flexible, since CO mixes evenly with air, but follow the model's instructions. Attached garages and rooms with a fireplace or gas appliance are the highest-risk spots and deserve their own alarm.
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