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Smoke and CO Alarms: Check Placement, Test, and Age

By Mark Phaneuf · Updated September 21, 2026 · Editorial policy

Check home alarms for four things: the right location, a passing test, a valid service life, and a clear exit plan. A light on the case does not prove all four. Make a small record for each smoke and carbon monoxide alarm so a missed battery or old sensor does not stay hidden.

If an alarm is sounding now, leave

Get everyone outside to fresh air. Call 911 or the fire department from outside. Do not search for the source, wait for symptoms, or go back in until responders say it is safe.

Carbon monoxide, or CO, has no smell or color. CPSC's CO guidance warns not to ignore an alarm. Headache, weakness, dizziness, or nausea can be warning signs too. Tell responders about possible exposure.

A low-battery chirp is not the same as a full alarm pattern. Learn the patterns from your manual before an event. If you cannot tell what the signal means, do not assume it is just a battery.

Map the alarms by room

For smoke alarms, USFA calls for units in each bedroom, outside each sleeping area, and on every level, including the basement.

For CO alarms, CPSC calls for protection on each level and outside sleeping areas. It gives separate limits for attics and basements without sleeping space. Follow local code and the exact model's placement rules; do not simply copy smoke-alarm locations.

Draw a simple floor plan. Mark each alarm with a number. Ask the local fire department about gaps, unusual ceilings, or where a CO unit belongs. Do not place a unit just because an old screw is there.

Put dates and models in one list

For each numbered alarm, record:

• Room and exact location.
• Brand and model.
• Smoke, CO, or combination type.
• Manufacture date.
• Battery or power type.
• Replace-by date from the instructions.
• Date and result of the last test.

USFA says smoke alarms should be replaced 10 years from their manufacture date. CO alarm life varies by model. Follow its replace-by date and end-of-life signal.

If a label is too high to reach safely, get help. Do not balance on furniture or remove a hardwired unit to chase a date. A missing date is a reason to check with the maker or fire department.

Test monthly using the button

CPSC recommends monthly tests. Tell the household before you start, then use the test button as the maker directs. Do not use a flame, car exhaust, or an improvised smoke source.

The CO test button checks the alarm's circuit, not the accuracy of its sensor. A passing test does not extend its service life.

Record whether the expected units sound and can be heard where people sleep. If an alarm fails, follow its troubleshooting steps and restore protection promptly. If you cannot fix it safely, get help.

For people who cannot hear a normal alarm, ask about alarms with lights or bed-shaking devices. Also plan who helps children or anyone who needs help to leave.

Treat batteries and wiring as different jobs

Use the battery type and replacement schedule in the manual. Never take a battery out just to stop an unwanted alarm. Find and fix the cause while keeping protection in place.

Do not open a sealed battery unit to change its battery. Replace it as its instructions require. A hardwired alarm can still have a backup battery and an expiry date.

Have a qualified electrician handle hardwired installation and faults. Do not open electrical boxes. Our breaker guide and hot or buzzing outlet guide explain other reasons to stop using affected equipment.

Practice the response, not just the sound

Choose an outside meeting place. Plan two ways out of rooms where possible. Decide who will help children, guests, or adults who need support. Do not send anyone back inside for belongings or pets.

Keep the alarm map with your home maintenance plan. Put the next monthly test and replace-by dates on the calendar.

After a test, close the record with one clear result: passed, fixed, or service booked. “Will check later” is not a working alarm plan.

Quick answers

What should I do if a smoke or CO alarm sounds?

Get everyone outside and call 911 or the fire department from outside. Do not search for the source or go back in until responders say it is safe.

When should a smoke alarm be replaced?

USFA says to replace smoke alarms 10 years from the manufacture date. Follow any earlier replacement or failure warning in the model's instructions. A new battery does not renew an old sensor.

Do smoke and CO alarms use the same placement rules?

No. Smoke alarms belong in bedrooms, outside sleeping areas, and on each level, including the basement. CO placement has its own model and local-code rules. Ask the fire department if the layout is unclear.