How to test smoke and carbon monoxide detectors

The short answer

The U.S. Fire Administration says to test smoke alarms monthly. It takes a few minutes for a whole house: press the test button on each one and listen for the full alarm. Do your carbon monoxide (CO) alarms on the same day. CPSC says to follow the maker's instructions for CO alarms, and the test button works the same way on most of them.

The monthly test tells you an alarm can still sound. Alarms also wear out with age, so the replacement dates below matter as much as the test itself.

How to test smoke and CO alarms

1. 1. Tell the house firstLet everyone know a loud test is coming, and warn anyone with a pet that startles.
2. 2. Press and hold the test buttonHold it until the alarm sounds. It may take a few seconds. A broom handle works for a ceiling alarm you can't reach.
3. 3. Listen for a full, loud alarmA weak or no sound means a dead battery or a failed alarm. Change the battery if it has one and test again. If it still fails, replace the alarm.
4. 4. Check linked alarmsIf your alarms are interconnected, have someone confirm the others sound too when you test one.
5. 5. Read the date on the backOnce a year, look at the manufacture date. Smoke alarms past 10 years, and CO alarms past their maker's life, get replaced.
6. 6. Write it downNote the date of the test and anything you replaced, so next month's check starts from a record.

Where the alarms go

• Smoke alarmsUSFA says inside each bedroom, outside each sleeping area, and on every level of the home, mounted on the ceiling or high on the wall.
• CO alarmsCPSC says on every level of the home and outside sleeping areas. Keep them away from heating vents and anywhere furniture or drapes could cover them, and not in kitchens or directly above fuel-burning appliances.
• InterconnectedBoth USFA and CPSC favor alarms that are linked, so when one sounds, they all sound. You hear a basement alarm from a bedroom.

What Illinois requires

If you live in Illinois, the State Fire Marshal's fact sheet on the Smoke Detector Act says one- and two-family homes need a smoke alarm within 15 feet of every room used for sleeping and on every story, including basements but not unoccupied attics. Since January 1, 2023, homes still using alarms with removable batteries must switch to alarms with 10-year sealed batteries. Illinois has also required CO detectors within 15 feet of rooms used for sleeping since January 1, 2007, in homes that use fossil fuel to cook, heat or make hot water. Outside Illinois, check your state's rules, which differ.

Batteries

For alarms with a replaceable 9-volt battery, USFA says to change the battery at least once a year. Hardwired alarms have a backup battery, and that one gets changed at least once a year too. Alarms with a sealed 10-year battery have nothing to change: you replace the whole alarm when it reaches its end of life. A chirp every so often usually means a low battery or an alarm at end of life. Your model's manual says which.

When to replace them

Smoke alarms: USFA says to replace the entire alarm every 10 years, counted from the manufacture date printed on the back, not the day you put it up.

CO alarms: CPSC says to get the replacement age from the product literature or the maker. Kidde, for example, says its CO alarms last 7 to 10 years depending on the model: most made from 2013 on have a 10-year life, and units made before 2013 have a 7-year life. Kidde's alarms signal end of life with a beep every 30 seconds that keeps going after new batteries, or an ERR or END code on digital models. A CO alarm in end-of-life mode no longer protects you, so replace it.

Hardwired and interconnected alarms

Many newer houses have alarms wired into the house's electrical system and linked together. USFA says only a qualified electrician should install hardwired alarms. When one reaches its replacement date, check its manual for a compatible replacement, and call an electrician if the wiring or connector doesn't match.

If a CO alarm sounds

CPSC's guidance: never ignore it, and don't go looking for the source. Get everyone outside into fresh air, call 911 or the fire department from outside, and count heads. Don't go back in until emergency responders say you can. If an appliance was the cause, don't use it again until a trained technician has serviced it. If the alarm goes off again within 24 hours, repeat those steps and have a qualified technician check all your fuel-burning equipment. Early CO poisoning feels like the flu without the fever: headache, fatigue, shortness of breath, nausea, dizziness.

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