How to test a smoke and carbon monoxide alarm
Test a smoke or carbon monoxide alarm by pressing and holding its test button until it sounds, once a month. Replace batteries once a year unless it has a sealed long-life battery, and replace the whole alarm by the date printed on it, usually ten years for smoke alarms. If a carbon monoxide alarm goes off for real, get everyone outside and call your local emergency number, 911 in the US.
Why it matters: It is the most skipped two-minute check, and the one that matters at night.
Steps
- Find every alarm. Smoke alarms go in each bedroom, outside sleeping areas and on every level; carbon monoxide alarms go outside sleeping areas and on every level.
- Press and hold each test button until the alarm sounds loudly.
- Check the date on the back and replace any alarm past its replace-by date.
- Replace batteries every year on a date you will remember, unless the battery is sealed.
- Vacuum dust from the vents gently.
- Ask the landlord in writing to fix or replace any alarm that fails.
- If a carbon monoxide alarm sounds, go outside at once, then call your emergency number from outside.
Stop and call a professional if
- a carbon monoxide alarm sounds, or anyone has headache, dizziness or nausea at home: get outside and call your local emergency number, 911 in the US
- an alarm is hard-wired and fails the test: ask the landlord or an electrician; do not open the wiring
Common mistakes
- Removing the battery to stop kitchen false alarms.
- Assuming a lit light means the alarm works.
- Ignoring a chirp, which usually means a low battery or an alarm at the end of its life.
Teach this to someone
A one page sheet for showing a friend, a teenager or a parent: what to say, what to show, and one question to check it landed.
Teach: How to test a smoke and carbon monoxide alarm
What to say
Test a smoke or carbon monoxide alarm by pressing and holding its test button until it sounds, once a month. Replace batteries once a year unless it has a sealed long-life battery, and replace the whole alarm by the date printed on it, usually ten years for smoke alarms. If a carbon monoxide alarm goes off for real, get everyone outside and call your local emergency number, 911 in the US.
What to show
- Find every alarm. Smoke alarms go in each bedroom, outside sleeping areas and on every level; carbon monoxide alarms go outside sleeping areas and on every level.
- Press and hold each test button until the alarm sounds loudly.
- Check the date on the back and replace any alarm past its replace-by date.
- Replace batteries every year on a date you will remember, unless the battery is sealed.
- Vacuum dust from the vents gently.
- Ask the landlord in writing to fix or replace any alarm that fails.
- If a carbon monoxide alarm sounds, go outside at once, then call your emergency number from outside.
Where it stops
Stop and call a professional if a carbon monoxide alarm sounds, or anyone has headache, dizziness or nausea at home: get outside and call your local emergency number, 911 in the US.
Check question
Which habit catches a dead smoke alarm before you need it?
Answer: Holding its test button until it sounds, once a month. A monthly test is the only way to know it still works.
Your checklist
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Quick quiz
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Related skills
Sources
- US national fire protection guidance on smoke and carbon monoxide alarms, 2026. Reviewed September 28, 2026.
Written in our own words from the sources above. It is general information, not advice for your situation; where a professional, your doctor or your lease says something different, follow them.
Last reviewed . First published .