Fresh batteries don't fix an expired alarm. Internal sensors degrade after roughly 10 years even when the test button still triggers the speaker. Most homeowners track the battery and ignore the unit. Here's how to find the manufacture date, when to replace, and how to remember a decade from now.
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Not from purchase. Not from install. From the date stamped on the back.
maximum service life NFPA recommends for any smoke alarm
National Fire Protection Association
recommended lifespan for combination smoke and CO alarms
First Alert, Kidde manufacturer guidance
typical cost of a single replacement alarm — far less than the consequence
Hardware store retail pricing
Smoke alarms detect smoke in one of two ways. Ionization alarms use a tiny amount of radioactive material to monitor air conductivity. Photoelectric alarms shine a beam across a chamber and watch for scattered light when smoke enters. Both rely on a sensor that degrades with time, dust accumulation, humidity, and exposure to cooking byproducts.
After about 10 years, the sensor's response time slows. The alarm may still trigger eventually — but "eventually" in a fire is too late. The test button only confirms the speaker and battery work, not that the sensor still detects smoke at the speed it did when it was new. That's the gap nobody talks about.
Twist counter-clockwise off the mounting bracket. For hardwired alarms, also disconnect the wiring harness from the back.
Most alarms show a clear "MFG" or "Manufactured" date in YYYY-MM format. First Alert and BRK use a sticker; Kidde often molds it into the plastic.
If the manufacture date is more than 10 years old, replace the unit today. If you cannot find any date, assume it's expired — the alarm is old enough that the date stamp wasn't required, which means it's old enough to replace.
When you put up a new alarm, mark the install date on the side with a permanent marker. Future you (or the next homeowner) will know exactly when the 10-year clock runs out.
Sealed 10-year alarms have a non-replaceable lithium battery built into the unit. They are designed to run for a decade with no battery changes, then chirp at end of life and be replaced whole. For households that consistently forget battery swaps, these are the safest choice — the only thing to remember is the one-time replacement at the 10-year mark.
That single 10-year reminder is exactly the kind of long-horizon task most calendar apps can't carry forward. An email reminder set to your install date plus 10 years lands in whatever inbox you're using a decade from now. Set it once, the day you install the alarm, and forget about it.
There are three reminders worth setting for smoke detectors. Battery changes every six months. A monthly test press (the easiest one to skip). And the 10-year unit replacement, which most homeowners never set at all.
The pillar guide covers the battery cadence in full — smoke detector battery reminder. The chirping page covers what to do when the alarm starts complaining — smoke detector chirping after battery change. This page is for the one homeowners forget: the unit itself.
Yes. The NFPA recommends replacing every smoke alarm at least every 10 years. The internal sensors — ionization or photoelectric — degrade over time. After roughly a decade, the alarm becomes less likely to detect smoke quickly enough to give you time to escape, even if it still beeps when you press the test button.
Take the alarm off the ceiling and check the back. Most manufacturers stamp the manufacture date directly on the housing — typically a date in the format "MFG 2018-04" or similar. If you only see a model number, look up the manual online or check the date code on the battery compartment label. If you cannot find any date, assume the alarm is over 10 years old and replace it.
Immediately. A 20-year-old alarm is twice past its rated service life. The sensors are likely too degraded to detect smoke reliably, even though the test button may still trigger the speaker. The cost of a new alarm is $15–$40. The cost of an alarm that fails to detect a real fire is everything else.
Yes, on the same 10-year schedule. Being wired to the home's electrical system has nothing to do with the sensor lifespan — the same internal components age at the same rate. Hardwired alarms typically come down by twisting counter-clockwise on the bracket. Disconnect the wiring harness and replace the unit with one that uses the same connector type.
Most alarms emit a different chirp pattern at end of life — typically every 30 seconds for several days, sometimes accompanied by a flashing red light. If you replaced the battery and the chirping continues after a reset, end of life is the most likely cause. Check the manufacture date on the back to confirm.
A 10-year reminder is hard to set on a calendar app you might not be using by then. A free email reminder set to your alarm's installation date plus 10 years works well — the email arrives wherever you read email at that future point. BoldRemind is built for exactly this kind of long-horizon reminder.
The hardest reminder to remember is the one a decade out. Set it now while the install date is fresh — we'll email you when it's time.
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