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Replace every smoke alarm 10 years from its date of manufacture — the date printed on the back of the unit, not the day you installed it. That is the National Fire Protection Association interval, and it applies to battery, hardwired, sealed, photoelectric and ionization alarms alike. Between replacements: test every alarm monthly, replace user-serviceable batteries once a year, and vacuum the vents when you dust. Carbon monoxide alarms run on a shorter clock, typically 5 to 7 years.
The reason the interval is fixed rather than condition-based is that there is no home method to verify the sensing element. The test button confirms the horn, the battery and the electronics — not the sensor. Model picks are in best smoke detector; we do not test devices first-hand, and the method is in how we rank.
Why 10 years, when the alarm still beeps?
Because the beep is not the part that expires. In a photoelectric alarm, the optical chamber slowly accumulates dust and film and the light source dims, both of which shift the threshold at which scattered light triggers the alarm. In an ionization alarm, the trace americium-241 source decays on its own schedule and the chamber contaminates. Neither failure produces a symptom you can see or hear. The alarm continues to sound its horn happily when you press test, because pressing test does not introduce smoke.
Ten years is the point at which manufacturers stop certifying that the sensor will respond within the timeframe UL 217 requires. It is also, conveniently, the interval that lines up with sealed ten-year lithium batteries, which is why sealed units have become the default recommendation: the whole device has one clock instead of two.
How do I find the date on my alarm?
Twist the alarm off its bracket — most rotate a quarter turn counterclockwise — and read the label on the back. You are looking for a date of manufacture, printed either in full or as a month and year. It sits near the model number and the UL listing mark.
Two things to note while it is in your hand. First, this is not the date on the box or the date you bought it: alarms sit in warehouses and on shelves, and it is entirely normal to buy one that is already a year or two into its ten. Second, if there is no legible date anywhere on the housing, the alarm predates the labeling requirement and is old enough to replace on that fact alone. Write your install date on the housing in permanent marker before you put it back, so the next person to stand on that chair does not have to work any of this out.
What is the full maintenance schedule?
| Interval | Task | Applies to |
|---|---|---|
| Monthly | Press and hold the test button until it sounds | Every alarm, smoke and CO |
| Every 6 months | Vacuum vents with a soft brush; check for insects | Every alarm |
| Annually | Replace the battery | Any alarm with a user-replaceable cell, including hardwired backups |
| 5–7 years | Replace the unit | Most carbon monoxide alarms |
| 10 years from manufacture | Replace the unit | Every smoke alarm, and sealed 10-year CO alarms |
Testing monthly sounds excessive until you time it: two minutes for a whole house. The interval matters because the failure mode being guarded against — a battery removed after a nuisance alarm and never put back — is invisible from the floor.
Should I replace them all at once?
Usually yes, because they almost certainly age together. Alarms installed by a builder or bought in a multipack all carry manufacture dates within weeks of each other, so a house that needs one replaced this month will need the rest within the year. Doing the whole set in one afternoon is cheaper per unit, keeps the interconnect chain to one manufacturer, and means the ten-year clock resets across the house on a single date you can write down.
It is also the natural moment to fix coverage gaps and sensor choice. Most American homes are short of the NFPA baseline of one alarm inside every bedroom, one outside each sleeping area and one on every level — the count is worked through in how many smoke detectors do I need. And if the alarms coming down are ionization units in bedrooms, replacing them with photoelectric or dual-sensor models is a genuine upgrade for night-time smoldering fires, explained in ionization vs photoelectric.
Does a hardwired alarm last longer?
No. Mains power keeps the alarm running, but it does nothing for the sensor, and hardwired units expire on exactly the same ten-year schedule. They still have a backup battery, which still needs annual replacement unless the model uses a sealed ten-year backup.
One practical warning for hardwired replacements: connector styles vary between brands and generations, and a twenty-year-old harness may not accept a new alarm without an adapter plug. Buy the same brand as the existing units where possible, keep the whole interconnected circuit on one manufacturer, and kill the breaker before disconnecting anything. If the panel is not somewhere you are comfortable working, that is the point to call a licensed electrician. In most jurisdictions a home built with hardwired interconnected alarms must keep them — you cannot substitute battery-only units — and requirements vary by state and city, so check yours. The trade-offs are in hardwired vs battery smoke detector.
What if it starts chirping before 10 years?
Then it is probably a battery, and the fix takes five minutes: replace the cell, hold the test button for 15 seconds with the battery out to drain the residual charge, reseat it. Dust, an unlatched battery door and a cold night that drops battery voltage account for most of the rest. The full decision tree is in why is my smoke detector chirping.
What you must not do is remove the battery and leave the alarm dead. NFPA data shows that almost three of every five home fire deaths occur in homes with no alarms or with alarms that failed to operate, and a missing battery is the most common single reason a present alarm does nothing.
How do I dispose of an old smoke alarm?
Photoelectric alarms are ordinary electronic waste and go in an e-waste stream or, in many areas, household trash. Ionization alarms contain a sealed trace amount of americium-241; the quantity is small and the source is sealed, but disposal rules vary. Some manufacturers accept old ionization units back by mail, and many municipal household hazardous waste programs take them. Check your local rules rather than assuming, and do not attempt to open the chamber. Remove and recycle batteries separately.
Where to go next
If you are replacing units now, the shortlist is in best smoke detector, combination smoke and CO units in best combination smoke and carbon monoxide detector, and standalone CO alarms — on their shorter 5 to 7 year clock — in do carbon monoxide detectors expire and best carbon monoxide detector. Everything else in the category is in the air quality hub.