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How to Test Smoke and Carbon Monoxide Alarms

Working smoke and CO alarms are the cheapest life insurance in your home. Here's how to test them monthly, when to replace them, and where they belong.

2 min read
In your maintenance planTest smoke & CO alarmsSee the cadence, priority, and steps for Smoke & CO alarms.

No maintenance task has a better return than this one: a few seconds a month protecting against fire and an invisible, odorless gas that kills. Testing your alarms costs nothing and is the most important critical task on your list.

Why both alarms matter

  • Smoke alarms give you the minutes you need to get out of a fire.
  • Carbon monoxide alarms catch a gas you can't see or smell — produced by furnaces, water heaters, gas stoves, fireplaces, and cars idling in an attached garage. CO poisoning is easy to mistake for the flu until it's dangerous.

Most homes need both, and many newer alarms combine the two in one unit.

The monthly test

  1. Press and hold the test button on each alarm until it sounds. A weak or absent alarm means a dead battery or a failed unit.
  2. Listen for chirping between tests — a single chirp every minute or so usually means a low battery, not a real alarm.
  3. Replace batteries the moment an alarm chirps, and at least once a year regardless (unless it's a sealed 10-year lithium unit).

A simple habit: test on the first of every month, or whenever you pay a recurring bill.

When to replace the whole alarm

Alarms don't last forever, even if they still beep:

  • Smoke alarms: replace 10 years from the manufacture date printed on the back.
  • CO alarms: replace every 5–7 years per the manufacturer.

If you can't find a date, it's old — replace it. Our maintenance plan flags alarms older than 10 years automatically.

Placement that actually protects

  • A smoke alarm in every bedroom, outside each sleeping area, and on every level (including the basement).
  • CO alarms on each level and near sleeping areas, especially close to an attached garage or fuel-burning appliances.
  • Interconnected alarms — where one triggers all — give the earliest warning, which matters most at night.

A two-minute upgrade

If your alarms are a mix of ages or you're not sure when they were installed, replacing them all with current 10-year sealed units is cheap peace of mind. While you're at it, make sure everyone in the home knows two ways out of each room.

Never miss the test

Build your free Owner Tools and we'll keep the monthly alarm test and the 10-year replacement on your schedule as the life-safety priorities they are — no login, no address required.

Frequently asked questions

How often should I test smoke and CO alarms?+
Press the test button on every alarm once a month. Replace the batteries at least once a year (unless they're sealed 10-year units), and replace the entire alarm every 10 years — sensors wear out even if the unit still beeps.
How do I know when to replace a smoke detector?+
Check the manufacture date printed on the back. Smoke alarms should be replaced 10 years from that date, and CO alarms typically every 5–7 years. An alarm that chirps intermittently usually needs a battery; one that won't pass a test or is past its date should be replaced entirely.
Where should smoke and CO alarms be placed?+
Put a smoke alarm in every bedroom, outside each sleeping area, and on every level including the basement. Carbon monoxide alarms go on each level and near sleeping areas, especially close to attached garages and fuel-burning appliances. Interconnected alarms that all sound together are safest.

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