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Yes. Carbon monoxide detectors expire, typically after 5 to 7 years, with some sealed models rated for 10. The part that expires is the electrochemical sensor, not the battery: it contains an electrolyte consumed by normal operation that slowly dries out, so the alarm degrades on a calendar whether or not it has ever detected anything. The date is printed on the back of the unit. Past it, the alarm chirps a signal that no battery will stop and that most models will not let you permanently silence — because the manufacturer can no longer certify it will respond to CO in time.
This matters more than the equivalent question about smoke alarms, because carbon monoxide is colorless, odorless and tasteless. The CPSC calls it the Invisible Killer: there is no sensory backup if the device is dead. Model picks are in best carbon monoxide detector; we do not test devices first-hand — see how we rank.
Why does a CO sensor wear out?
Because it works by chemistry rather than optics. Inside a residential CO alarm is an electrochemical cell: two electrodes separated by an acidic electrolyte. Carbon monoxide entering the cell is oxidized at the working electrode, producing a small current proportional to concentration. That current is what the alarm measures.
The electrolyte is the consumable. It gradually evaporates through the diffusion vent, and it is degraded by heat and by long periods of very low humidity — which is exactly what a forced-air heated house delivers every winter. Repeated exposure to CO also consumes reagent. The result is a sensor whose output drifts downward over years until it can no longer be trusted to hit the UL 2034 response curve, and there is no way to detect that from the outside, which is why the interval is fixed rather than condition-based.
How long does each type last?
| Device | Typical service life | Clock starts |
|---|---|---|
| Plug-in CO alarm with battery backup | 5–7 years | Date of manufacture |
| Battery CO alarm, replaceable cells | 5–7 years | Date of manufacture |
| Sealed 10-year CO alarm | 10 years | Date of manufacture |
| Combination smoke and CO alarm | 7–10 years, whichever sensor is shorter | Date of manufacture |
| Smoke alarm, for comparison | 10 years (NFPA) | Date of manufacture |
Note the column on the right. Every one of these clocks starts at manufacture, not at purchase and not at installation. Alarms sit in warehouses and on shelves, so it is entirely normal to buy a five-year unit with four and a half years left. Check the date stamp before you install a new one, and reject anything that has clearly been sitting.
How do I tell an expired alarm from a low battery?
By the date on the label, not by the sound — and this is genuinely the most misdiagnosed noise in American homes. A low-battery chirp and an end-of-life chirp are similar enough that people spend an evening cycling 9V cells through an alarm that is simply too old, then conclude the batteries were bad.
Work through it in this order:
- Fit a fresh battery from a sealed package, hold the test button for 15 seconds with the battery out to drain the residual charge, then reseat it.
- If it still chirps, read the label on the back. Past the printed replace-by date, or more than 5 to 7 years past manufacture, the alarm is finished.
- Count the beeps. Many models use a distinct end-of-life pattern, and voice models announce it outright. A CO alarm is four beeps then a pause, repeating loudly — that is an emergency, not an expiry.
- Replace the unit. There is no repair, no reset, and no reason to spend more time on it.
The same troubleshooting for smoke alarms, which chirp for a wider range of reasons, is in why is my smoke detector chirping.
Can I silence it until I get a replacement?
Temporarily, on most models. Manufacturers commonly allow an end-of-life hush of several hours to a couple of days — enough to get a night's sleep — after which the signal returns and cannot be stopped again. That behavior is intentional. An alarm that could be permanently silenced at end of life would sit silently on a wall for years while the household assumed it was working.
What you should not do is take the battery out and leave it. Buy the replacement the same week. If you need a stopgap tonight, a cheap battery CO alarm costs about as much as a takeout meal and is worth keeping as a spare in any case — for hotel rooms, rentals and RVs where you have no idea what the heating is doing.
Why an expired CO alarm is a bigger gap than an expired smoke alarm
Because smoke gives you a second channel and carbon monoxide gives you none. You can smell smoke, see it, feel the heat. Carbon monoxide produces headache, nausea, dizziness and confusion — symptoms that are easily attributed to flu, and that impair judgment before they become obviously dangerous. Most fatal residential exposures happen to people who are asleep.
The sources are ordinary household equipment: a cracked furnace heat exchanger, a blocked flue, an unvented space heater, a gas range used for heating, a fireplace with an obstructed damper, a water heater backdrafting because a bathroom fan has depressurized the house, a car warming up in an attached garage — and above all a portable generator during a power outage. The CPSC attributes more than 200 accidental non-fire CO deaths a year to consumer products, with portable generators the single largest contributor, clustered in the days after storms. Never run a generator indoors or in a garage, and keep it at least 20 feet from any window, door or vent; our generator runtime calculator carries the same warning alongside the fuel math.
If an alarm sounds and anyone has symptoms, get everyone outside into fresh air and call 911 from outside. Do not stay to investigate. This page is about device lifespan, not medical advice.
Making the replacement date impossible to forget
Three habits cover it. Write the install date on the housing in permanent marker the day you mount it, so the ten-second question in five years' time has a ten-second answer. Set a calendar reminder for the replace-by date at the same time. And test every alarm monthly — which confirms the horn and the electronics but never the sensor, which is precisely why the date matters.
If you are replacing CO alarms now, take the opportunity to check coverage as well as age: the CPSC recommendation is one alarm on every level of the home and one outside each separate sleeping area, at least 15 feet from fuel-burning appliances and out of bathrooms. That is worked through in where to place a carbon monoxide detector. Smoke alarms run on their own ten-year schedule — see how often to replace smoke detectors — and if you would rather run one device for both, the trade-offs and the field are in best combination smoke and carbon monoxide detector. Everything else is in the air quality hub.