Around the house · First steps · about 15 minutes

Test Smoke and CO Alarms

Smoke alarms and carbon monoxide (CO) alarms are some of the cheapest life-savers in a home, but only if they work. Testing them takes a few minutes a month. Knowing their age, where they belong, and what to do when one sounds matters just as much.

When to teach it: Watch from about 5, help from about 8, do it alone from about 12.

You'll need

A sturdy step stool or ladder
Replacement batteries of the type printed on each alarm
Marker and paper
A helper to steady the ladder

Before you start

Read the instructions for each alarm. Mounting, testing, and replacement details can vary by model.

Step by step

Tick each step as you go if you like; ticks stay on this device.

Find every alarmWalk through the house and list each alarm. Smoke alarms belong inside each bedroom, outside each sleeping area, and on every level of the home, including the basement.
Press the test buttonPush each smoke alarm's test button. It should sound loudly. Do this once a month.
Fix a silent alarmIf an alarm doesn't sound, put in a new battery and test again. If it still doesn't sound, replace the alarm.
Check the dateLook on the back for the date it was made. Replace any smoke alarm that is 10 years old or older, even if it still beeps.
Change batteries on scheduleIf your alarms use replaceable batteries, change them at least once a year. Sealed 10-year alarms don't get new batteries; you replace the whole alarm when its time is up.
Test the CO alarmsTest CO alarms monthly. They belong outside sleeping areas and on every level of the home. Check the manual for when to replace them.
Learn the soundsA chirp from a smoke alarm usually means its battery is low; replace the battery right away. A loud, steady alarm means danger.
Practice the CO planIf the CO alarm sounds, everyone goes outside to fresh air right away, then you call 911. Nobody goes back in until emergency responders say it's safe.

Physics

How it works: Two ways to sense smoke, and one gas you can't

Ionization alarms hold a tiny, safely shielded amount of radioactive material. It lets the air between two metal plates carry a small electric current. When smoke drifts in, the particles grab the charged bits of air and carry them away, so the current drops. When it drops enough, the alarm sounds. These respond faster to fast, flaming fires.

Photoelectric alarms shine a light beam through a dark chamber, aimed so it misses a light sensor. When smoke drifts in, the particles scatter the light, and some of it bounces onto the sensor. These respond faster to slow, smoldering fires. Because no one knows what kind of fire might start, safety agencies recommend having both kinds, or dual-sensor alarms.

Carbon monoxide is a poisonous gas with no color and no smell. Your nose can't warn you, so a CO alarm has to.

replace-by year for a smoke alarm = year it was made + 10

Try it: In a dark room, shine a flashlight through the side of a clear glass of water. Then stir in a few drops of milk. Now you can see the beam, because the tiny milk droplets scatter the light. A photoelectric alarm uses the same idea with smoke.

Keep learning: Science

Teaching it to your kids

Let your child press the test button while a grown-up steadies the ladder, so they know the sound.
Teach the difference: a chirp means 'change my battery'; a loud, steady alarm means 'get out'.
Make a chart of every alarm, where it is, and its replace-by year.
Practice the CO plan: outside first, then call 911.

Tips

Pick an easy date for battery changes, like when you change your clocks.
Interconnected alarms are best: when one sounds, they all sound.
Mount smoke alarms on the ceiling or high on a wall, following the instructions. CPSC says wall alarms go about 6 to 12 inches below the ceiling.
If cooking sets off an alarm, open a window, press the hush button, or wave a towel. Never take out the battery.
A CO alarm's test button checks its circuits, not the accuracy of its sensor, so replace it on time.
There are alarms with strobe lights or vibration for people who are deaf or hard of hearing.

Common mistakes

Mistake	Instead
Pulling the battery because cooking keeps setting off the alarm.	Use the hush button, or move the alarm a few feet farther from the kitchen. Disabling an alarm can be a deadly mistake.
Keeping an old smoke alarm because it still beeps.	Replace smoke alarms 10 years from the date they were made.
Having alarms only in hallways.	Add one inside each bedroom too, and on every level.
Ignoring a CO alarm because nobody smells anything.	CO has no smell. Treat every CO alarm as real: go outside, then call 911.

Safe habits

If the CO alarm sounds, move everyone outside to fresh air right away, then call 911.
Stay out until emergency responders say it's safe to go back in.
Never disable a smoke alarm or take out its battery.
Test smoke alarms every month.

When to call a pro

Hardwired alarms, the kind wired into the house, should be installed by a qualified electrician.
If a CO alarm went off and you suspect an appliance, don't use that appliance again until trained service personnel have checked it.

Sources

Free how-to guides for families, with nothing to earn, pass or send in. They follow U.S. rules and sources; your owner's manual, product labels and state and local rules come first.