When to Actually Replace a Smoke Alarm (It's Not Just the Battery)
Every smoke alarm has a service life printed on the back, and most people never look. The sensor degrades with dust and age, so an alarm can chirp, pass a button test, and still fail to detect smoke. That's the failure mode that matters.
The replacement schedule
Ionisation and photoelectric alarms are typically rated for ten years from the manufacture date, not the install date. CO alarms often shorter — check the label.
| Device | Replace every | Test every |
|---|---|---|
| Smoke alarm (photoelectric) | 10 years | Monthly |
| Smoke alarm (ionisation) | 10 years | Monthly |
| CO alarm | 5–7 years | Monthly |
| Combined smoke/CO | 10 years or CO rating | Monthly |
| Heat alarm | 10 years | Monthly |
Battery vs sealed
Sealed 10-year-battery alarms exist precisely because people remove batteries from nuisance alarms. If you've ever taken a battery out because the alarm kept going off, replace the alarm or fix the source — don't run unpowered.
Placement that actually matters
One alarm per level at minimum, one in each sleeping area hallway, and one in each bedroom if doors are normally closed at night. Alarms mounted within 3 feet of a bathroom door false-alarm constantly; within 3 feet of a cooking appliance, likewise. That placement error is the main cause of removed batteries.
The date trick
Write the install month and year on the back with a marker when you mount it. Then you never have to guess, and the next person in the house doesn't either.
The mistakes that cost people money
- Replacing the battery forever and never the alarm.
- Removing a battery from a nuisance alarm and never restoring it.
- Mounting near the kitchen or bathroom and then disabling it.
- Testing with the button only — that checks the sounder, not the sensor.
Common questions
Does the button test prove the alarm works?
No. It proves the sounder and battery work. The sensor can still fail silently.
How do I find the manufacture date?
Printed on the back of the unit, usually as a date or a year-of-manufacture code. Not the date you installed it.