How often should you replace smoke detectors?
Updated July 2026
Replace every smoke alarm in the house every 10 years, measured from the manufacture date printed on the back, not the day you installed it. The sensing element degrades on a fixed clock whether the unit is ionization or photoelectric, so an alarm that still chirps and passes its test button can respond slowly, or not at all, to real smoke once it is past 10 years. Whole-home replacement is cheap insurance at $15–40 per unit, and it is the deadline homeowners most often miss.
What changes the interval
| Your situation | Interval | Why |
|---|---|---|
| Any alarm 10+ years past manufacture | Replace now | The sensor is beyond its rated, tested life |
| Battery-only alarms (9V or AA) | Every 10 years | Unit replaced whole; batteries yearly in between |
| Sealed 10-year lithium alarms | Every 10 years | Battery and unit are designed to retire together |
| Hardwired interconnected alarms | All at once | Mixed ages defeat interconnection; do the set together |
| Combination smoke/CO units | Per the shorter date | The CO sensor may age out at 5–7 years first |
| No legible date on the back | Replace now | Undatable means assume it is expired |
| After a kitchen fire or heavy smoke | Inspect, likely replace | Soot and heat can compromise the sensor |
The cost of skipping it
What skipping it costs: the price is measured in minutes and lives, not dollars. US fire agencies consistently find that a large share of home fire deaths happen in homes with no working smoke alarm, and an expired detector counts as not working even though it looks armed. Modern fires flash over in as little as 3–5 minutes, far faster than the furnishings of decades past, so a slow or silent alarm erases the escape time you are counting on. Redoing the whole house runs $15–40 per unit; interconnected sets a bit more. There is no cheaper safety upgrade.
How to do it (10 minutes per alarm · DIY)
- Take each alarm down and read the manufacture date molded into the back; anything 10 years or older gets replaced.
- Match the type: standalone battery, sealed 10-year lithium, or hardwired interconnected with a matching connector.
- For hardwired units, switch off the breaker, unclip the old alarm, and plug the new base into the same harness.
- Mount alarms on every level, inside each bedroom, and outside each sleeping area, per current code.
- Press and hold test until it sounds, and if interconnected, confirm the others chime too.
- Write the install date inside the cover and set a 10-year reminder so the next cycle does not slip.
Knowing the interval is the easy half. OnOtto reminds you at the right interval, and it won't let you snooze it into next year. Tasks persist until they're done, and completing smoke alarm replacements schedules the next one automatically.
Put this on autopilot, free for 30 daysFrequently asked questions
If my smoke alarm still beeps when I test it, why replace it at 10 years?
The test button only proves the horn, battery, and circuit work; it does not test the smoke sensor's sensitivity. That sensing chamber slowly loses the ability to detect actual smoke particles as it collects dust and its components age, and there is no home test for that decline. Manufacturers and fire agencies settled on a firm 10-year replacement precisely because a healthy-sounding alarm can still be blind to a real fire. When the date says 10, it goes.
Ionization vs photoelectric: which should I buy?
Photoelectric alarms respond faster to smoldering fires from upholstery, wiring, and mattresses, while ionization alarms react a touch faster to fast-flaming fires. Because a home can have either kind, fire safety groups recommend covering both, either with dual-sensor alarms or by mixing types through the house. Whatever you choose, replace the whole set on the same 10-year clock so no room is left with an aged sensor. Then test them monthly.
Should I replace all the smoke detectors at once or as each one ages out?
If they were installed together, replace them together: they share a manufacture era, so when one hits 10 years the rest are close behind, and staggering the work usually means forgetting the stragglers. Interconnected hardwired systems especially should be done as a set, since a mix of old and new units can cause false alarms and communication faults. Buying a multipack of the same model also keeps batteries and test routines consistent across the house.