How often should you test smoke and carbon monoxide alarms?

Short answer

Test the smoke and CO alarms once a month. Press and hold the test button on every alarm in the house until it sounds, which takes 5 to 10 minutes for a whole home and costs nothing. While you're looking up at each one, read the date on its back or its label: an alarm older than 10 years is due for replacement no matter how it tests.

Why it matters

A smoke alarm is the one thing in the house that only has to work once. Fires at night spread through a home in minutes, and the alarm's job is to wake you in time to get out. A carbon monoxide alarm does the same for a gas you can't see or smell, which comes from a cracked furnace heat exchanger, a blocked flue, a car left running in the garage, or a generator too close to a window. Neither alarm gives any sign it has stopped working. The battery dies, the sensor ages, dust clogs the chamber, and the alarm sits there looking the same as it did when it was new.

The test button is the only way to know. It runs the alarm through its horn and its circuitry, and a healthy alarm answers with a loud, steady tone. Monthly is often enough to catch a dead battery before the chirping starts, and seldom enough that the household doesn't tune out the sound.

When to do it more often

The schedule has no modifiers, because monthly is already the floor. The additions are events rather than conditions: test every alarm after a power outage, since hardwired alarms with backup batteries sometimes come back in an odd state, after any work on the electrical system, and after you've moved into a new home, where you don't know when the alarms were last touched. If an alarm has gone off for cooking smoke, test it afterward to be sure it reset.

What you need

• A step stool, or a broom handle for alarms on high ceilings, since the test button on most alarms can be pressed with the end of a handle

Steps at a glance

1. Tell the household you're testing, so nobody panics or ignores a real alarm later.
2. Press and hold the test button on the first alarm until it sounds, and listen for a loud, steady tone.
3. For interconnected alarms, check that the others in the house sound along with it.
4. Move through every alarm: each bedroom, the hallway outside them, every level of the house, and the CO alarms near sleeping areas and the furnace.
5. Read the manufacture date on the back of each alarm as you go.
6. Note any alarm that was quiet, weak, or older than 10 years.

You're done when every alarm has sounded at full volume and none is past its date.

Signs it's overdue

• No sound when you press the test button, or a weak, warbling one.
• Chirping, which is a low battery, and comes every minute or so.
• An alarm with a date older than 10 years on the back.

DIY or pro

Testing alarms is the easiest job in the house, and it's meant to be done by whoever lives there. Nobody sells it as a service. The whole thing is a walk through the house with a step stool.

Where a professional comes in is on the wiring side. Hardwired alarms that won't test, that keep going off together with no smoke, or that chirp with fresh batteries can have a wiring fault or a failed unit in the chain, and an electrician sorts that out when replacing them. A CO alarm that sounds for real, with nobody feeling ill, still means leaving the house and calling the gas company or the fire department, not a technician.

FAQ

How do you test a smoke alarm?

Press and hold the test button until it sounds. A loud, steady tone means it works. Silence or a weak sound means the battery or the alarm needs replacing.

Why is my smoke alarm chirping?

A single chirp every minute or so is a low battery. Replace it. If the chirp continues with a new battery, the alarm itself is at the end of its life.

Should I test with real smoke?

No. The test button exercises the whole alarm. Smoke from a match or a candle fouls the sensor and can set off every alarm in the house.

How long do smoke alarms last?

About 10 years for smoke alarms. The sensor degrades whether or not the alarm has ever gone off, so the manufacture date on the back is what counts, not the test.