Smoke and CO alarms: test monthly, replace at ten years
This is the cheapest thing in the house that can save a life, and the easiest to forget, because a dead alarm looks exactly like a working one.
The four numbers
| What | How often |
|---|---|
| Press the test button | every month |
| Replace a 9-volt battery | at least once a year |
| Replace the whole alarm | 10 years from the manufacture date |
| Check the manufacture date | once — right now, on every alarm you own |
The ten-year rule is about the date on the back
Alarms are replaced ten years from the manufacture date printed on the unit, not from the day you put it up. A sensor that has been sitting in a warehouse and then on your ceiling since 2013 is out of service life, whatever it sounds like when you press the button.
Take one down and look at the back. If there is no date at all, it predates the labeling requirement and it is definitely old enough to replace.
Where they go
- Inside every bedroom. Someone asleep behind a closed door will not hear a hallway alarm reliably.
- Outside each separate sleeping area — the hallway serving the bedrooms.
- On every level, basement included.
- Smoke alarm — inside each bedroom, outside sleeping areas, every level
- Interconnected — a basement fire has to wake someone upstairs
- CO alarm — separate job near fuel-burning appliances and attached garages
Interconnected beats standalone. When one sounds, all sound. A fire that starts in the basement has to wake the person on the second floor, and only an interconnected set does that dependably. Wireless interconnected alarms exist for houses that were never wired for it.
Carbon monoxide is a separate job
If anything in the house burns fuel — gas furnace, water heater, range, fireplace — or if there is an attached garage, you need CO alarms as well. Carbon monoxide has no smell and no color; detection is the only warning you get. Combination units exist, but check the expiry on both functions, since CO sensors often carry a shorter rated life than smoke sensors.
Where to stop and call someone
Battery swaps and battery-powered units are homeowner work. Hard-wired alarms sit on house circuits: if you are replacing one and are not confident about killing the right breaker and verifying it is dead, that is an electrician's job. And a CO alarm that goes off is not a maintenance task at all — leave, then call the fire department from outside.
Questions people actually ask
How often should I test a smoke alarm?
Every month. It takes ten seconds with the test button, and it is the only way to know the alarm still works — a dead alarm looks exactly like a live one.
When do smoke alarms expire?
Ten years from the manufacture date printed on the back of the unit, not from the day you installed it. After that the sensor is past its rated life and the whole alarm gets replaced.
Where do smoke alarms have to go?
Inside every bedroom, outside each separate sleeping area, and on every level of the home including the basement. That is the standard layout in USFA and NFPA guidance.
What does interconnected mean, and does it matter?
When one alarm sounds, all of them sound. It matters because a fire starting in the basement should wake someone sleeping two floors up, and a single alarm at the source will not do that reliably.
Do I need carbon monoxide alarms too?
If you have any fuel-burning appliance — gas furnace, water heater, stove, fireplace — or an attached garage, yes. CO is odorless, and an alarm is the only way to detect it.
Sources
- U.S. Fire Administration (FEMA) — Smoke Alarms: monthly testing, annual battery replacement, ten-year replacement from manufacture date, placement, interconnection.
- U.S. Consumer Product Safety Commission — Smoke Alarms: Why, Where, and Which: placement by room and level, alarm types.
- CPSC — CO Alarms: where carbon monoxide alarms are needed and how they differ.
General information, not a substitute for local fire code — some jurisdictions require more alarms than the minimum above.