Short answer
Replace smoke detectors no later than 10 years from the manufacture date printed on the back, as NFPA 72 and manufacturers specify. The date is when the unit was made, not when it was installed. Replaceable batteries should be changed at least once a year, while sealed-battery alarms are replaced as a whole unit.
In this article
How often should smoke detectors be replaced?
Smoke detectors should be replaced no later than 10 years from the date of manufacture. That interval comes from NFPA 72, the national fire alarm code, and from manufacturers' instructions. The sensor degrades with age and contamination, so an older alarm may respond late or not at all even when its test button still works.
The ten-year clock starts when the alarm was made, not when it was installed. A unit that sat in a warehouse or a drawer for a while has already used part of its life before it reaches the ceiling, which is one reason to check the date on a new alarm before installing it.
Combination smoke and carbon monoxide alarms follow the manufacturer's stated life for the whole unit, which can be shorter than ten years because the carbon monoxide sensor wears out on its own schedule.
Where is the expiration date on a smoke detector?
Most smoke detectors have a date of manufacture printed on a label on the back, visible once the alarm is twisted off its mounting base. Some also print a replace-by date. If there is no date, or it is unreadable, treat the alarm as older than ten years and replace it.
Some newer alarms also show an end-of-life warning, usually a distinct chirp pattern or an indicator light that begins near the ten-year mark and does not stop when the battery is changed. The meaning of each pattern is in the manufacturer's manual and often on the label itself.
Writing the installation date on the alarm in marker is a common habit and a useful one, but the manufacture date on the label is the one that counts.
How often should smoke detector batteries be changed?
Alarms with replaceable batteries need a new battery at least once a year, or sooner if they chirp for low power. Alarms with sealed long-life batteries never get a battery change; the whole unit is replaced at the end of its life. Hardwired alarms also have backup batteries that need the same yearly attention.
A single chirp every minute or so usually means a low battery, though it can also signal end of life or a fault. Our guide to why a smoke detector keeps chirping walks through how to tell those signals apart. Testing every alarm once a month with its test button catches most dead batteries before they become a problem.
What are the signs a smoke detector needs replacing early?
Replace a smoke detector before ten years if it fails its test after a fresh battery, keeps chirping after the battery is changed, shows an end-of-life signal, or sounds false alarms that cleaning does not fix. Also replace alarms that were painted over, damaged, or exposed to heavy smoke, fire, or renovation dust.
Paint and construction dust are the two causes that most often go unnoticed. A coat of ceiling paint can seal the sensor openings, and drywall dust settles inside the chamber where it can block smoke or trigger repeated alarms. Covering alarms during work and removing the covers afterward avoids both.
Should all smoke detectors be replaced at the same time?
In most homes, yes. Alarms installed together reach their replacement date together, and interconnected alarms generally need to come from the same compatible line to keep sounding as one system. Replacing them as a set avoids a mix of ages and models, and resets a single date for the next replacement.
Mismatched replacements are a common reason an interconnected smoke alarm network stops working as one. In a monitored system, detectors also have a service life, and they are typically replaced and tested by the technician who maintains the panel; see what that service covers on our fire alarm monitoring page. For how replacement fits into overall upkeep of smoke and carbon monoxide devices, see our overview of smoke and carbon monoxide detectors.