How Long Do Smoke Detectors Last? (And How to Check Yours)
By the DC Fire & Security engineering team — installing and maintaining fire and security systems since 2010. Updated June 2026.
Quick answer
Ten years is the working life of a smoke detector — domestic alarms and most commercial detector heads alike. The sensing chamber degrades with dust, humidity and age, raising false alarms and slowing real response. Check the date of manufacture printed on the back of the unit: past ten years, replace it, even if the test button still beeps.
Why detectors expire when the button still works
The test button proves the battery, sounder and circuitry — not the sensor. Optical chambers accumulate contamination that both desensitises them to real smoke and triggers phantom alarms; the radioactive source in old ionisation units decays; seals and electronics age. Manufacturers' ten-year life is based on sensor drift, which the button cannot measure. An alarm that chirps innocently and passes its button test can still be functionally blind.
How to check and what to do
- Twist the alarm off its base and read the back: date of manufacture and/or replace-by date are printed on every unit
- No visible date and you didn't fit it? Treat it as expired
- Replace domestic alarms with sealed 10-year lithium interlinked units — no battery changes for life, one replacement event a decade
- In rented property, expired alarms fail the 'working alarm' duty even if they beep — check dates at tenancy turnover
- Commercial systems: detector head replacement around the 10-year mark is standard maintenance planning under BS 5839-1; addressable analytics (drift compensation warnings) flag heads going early
What replacement costs
Domestic: quality sealed 10-year alarms run £15–£40 each; a typical 3-bed LD2 set (two smoke, one heat, one more smoke for the living room, radio-interlinked) lands around £100–£200 in parts, fitted in an hour or two. Commercial: detector heads are typically £20–£60 each at scale, and planned wholesale head replacement at year ten is dramatically cheaper than the false-alarm churn, call-outs and degraded protection of running heads into their teens. We fold head-age tracking into maintenance contracts so replacement arrives as a plan, not a surprise.
Frequently Asked Questions
Do heat detectors and CO alarms expire too?
Is there any maintenance that extends detector life?
My alarms are mains-powered — do they still expire?
How do I dispose of old smoke alarms?
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