How often should you replace a smoke detector's battery and the unit itself?

The short answer

Two different things wear out on a smoke alarm, on two different schedules. The battery needs replacing every year (or, on sealed long-life models, not separately at all — it goes out with the unit). The unit itself — the sensor, the electronics, the alarm — needs replacing every 10 years, regardless of how good the battery still is. Kidde, First Alert and Bosch all publish that same 10-year figure for the unit, independently of each other.

Unit replacement: 10 years, no exceptions

Kidde is direct about it: "Kidde recommends replacing smoke and heat alarms every 10 years... according to the National Fire Protection Association (NFPA)." First Alert states the same thing about its own alarms: "smoke alarms should be replaced every ten years... every smoke alarm in your home has an expiration date." Bosch's smart smoke alarm carries the identical figure, tied to a cited standard rather than just company policy: "smoke alarms, especially those with optical measuring chambers, should be replaced no later than 10 years after commissioning," because "dust and other particles can accumulate in the measuring chamber," which reduces sensitivity.

Check the manufacture date printed on the back or inside the alarm's case — not the install date — and count 10 years from there. If you can't find a date at all, replace it; an undated alarm is itself a sign it's overdue.

Battery replacement: depends on the alarm type

This is where the two schedules diverge, and it depends on which kind of alarm you have:

• Removable-battery alarms (typically 9V): Kidde recommends replacing the battery "at

least once a year, or any time the unit indicates that the battery is low," and suggests tying it to a fixed date you won't forget — the daylight-saving clock changes are the reminder Kidde itself proposes.

• Sealed 10-year-battery alarms: the battery is built in and not designed to be replaced

separately — when it runs down, the whole unit is replaced, which is why these models are timed so the battery's life and the unit's life land together.

• Bosch's hardwired smart alarm with backup battery: the backup battery "typically lasts

about 5 years," shorter than the unit's 10-year life, so it gets one mid-life battery swap before the whole unit is due for replacement.

Whichever type you have, a low-battery chirp overrides the calendar — replace the battery (or the unit, if it's a sealed model) as soon as you hear it, not on the next scheduled date.

What the European standard actually requires

EN 14604, the harmonised European standard for household smoke alarms, doesn't itself hard-code "10 years" as a number printed in the regulation — what it requires is that the alarm carry a recommended replacement date on the device and warn the user audibly or visibly once that service life is reached or approaching. In practice, every major manufacturer's stated replacement life lands on 10 years, which is why it functions as the de facto standard even though the requirement itself is about labelling and end-of-life warning, not a fixed number. This detail comes from a manufacturer's own explainer of the standard, not the standard's published text itself (EN 14604 is a paid CEN document), so treat the "why 10 years specifically" reasoning as industry consensus rather than a quoted regulation.

Testing in between

None of this replaces testing. First Alert's own guidance calls for testing weekly — press the test button and confirm the alarm sounds. If it doesn't, don't wait for the replacement date: swap the battery first, and if that doesn't fix it, replace the unit regardless of its age.

Don't confuse this with CO alarm intervals

If your household also has a carbon monoxide or combination smoke/CO alarm, its clock runs differently — Kidde states 7–10 years depending on the model, and First Alert states most CO alarms "expire after 7 years." Track it as a separate item with its own interval; don't assume it matches your smoke alarm's 10-year date just because they hang on the same wall.

Before you rely on this

This isn't a Greek or EU legal mandate for private homes — no source checked here states that Greek law requires a private residence to install or replace smoke alarms on a fixed schedule (unlike, for instance, fire extinguishers in certain categories of building). It's manufacturer guidance, consistent across three independent brands and aligned with what EN 14604 requires to be labelled on the device. Always check the date printed on your own alarm rather than assuming it matches these figures — different models, and older stock, can carry a different service life.

Track it in Epimeleia

Add each smoke alarm as an item under your property, note the manufacture date from its label, and set a 10-year service interval for the unit plus a separate annual reminder for the battery. Both reminders arrive on schedule, so neither one depends on remembering a date printed on the inside of a plastic case you'll only look at once.