Many alarms sit on shelves for years before install. Look at the date printed on the back of the unit. Past 10 years = replace, no negotiation. CO sensors actually go bad faster (7-10 yrs).
The three tests
1. Monthly button test (30 seconds)
Press and hold the TEST button. Alarm should sound for 3-5 seconds. If interconnected (wired or wireless), every other alarm in the house should also sound within 10 seconds. Tests the circuit, battery, and horn — not the sensor.
2. Annual real-smoke test
Smoke alarm test aerosol (Home Safeguard 25S, ~$10 Amazon) is the right tool. Spray for 2 seconds at the alarm vents from below. Alarm should sound within 20 seconds. This tests the actual sensor chamber — the part the button test skips. Annual cadence. Document the date on the alarm with a Sharpie.
If the alarm doesn't sound on aerosol, the sensor chamber is fouled or dead. Replace the unit. Don't try to clean the chamber — sensors are sealed and don't unfoul.
3. 10-year manufacture-date check
Remove the alarm from the mount. Manufacture date printed on the back. 10 years from THAT date — replace the entire unit. Even if it still passes the test. The photoelectric sensor and electrochemical CO cell degrade. NFPA's mandate isn't optional.
Interconnect verification
NFPA 72 requires interconnected alarms in new construction (and in remodel work post-2014 in most jurisdictions). When one trips, every other alarm in the house trips. Verify the interconnect annually by triggering one alarm with aerosol and confirming every other alarm sounds within 10 seconds. If they don't, the interconnect is broken. Wired interconnect: an electrician chases the orange interconnect wire. Wireless (Kidde RF, First Alert SC5): re-pair the alarms in the app, or replace if a unit is at end-of-life.
For deep sleepers and hearing-impaired: the bedroom shaker
Standard smoke alarm horn is 3 kHz. NFPA research found that 520 Hz low-frequency alarms wake hearing-impaired, alcohol-impaired, and deep sleepers when 3 kHz horns don't. The Lifetone HLAC151 ($180-$220) is a bedside listener that picks up the T3 horn pattern from any UL-217 alarm and triggers a 520 Hz alarm + flashing FIRE display + bed shaker. If anyone in your house is over 65, hearing-impaired, on sleep meds, or a heavy sleeper, this is the missing piece.
FAQ
How often should I test smoke alarms?
Monthly button + annual real-smoke + replace at 10 years from manufacture. NFPA: 38% of US fire deaths in homes with no working alarms.
Is the test button enough?
Tests circuit + battery + horn. Does NOT test sensor chamber. Annual real-smoke test is the real verification.
Why does my alarm chirp once a minute?
Three causes: low battery, end-of-life (10+ yrs), or fouled sensor. Don't disable — replace.
How do I know when to replace?
10 years from MANUFACTURE date (printed on back), NOT install date. CO sensors fail faster (7-10 yrs).
Related guides
- Best smart smoke + CO combo alarms 2026 — 5 picks ranked
- Smoke alarm chirping every 30 seconds — the diagnostic
- Best smart smoke alarms 2026 — smart-feature comparison
Editorial standards: Cited authorities include NFPA 72 (National Fire Alarm and Signaling Code), NFPA 2024 home fire safety report, UL 217 (Smoke Alarms standard). Reviewed by Al, Building Doctor — SFFD Fire Safety Director (2001), IUOE Local 39.