How to Test Your Carbon Monoxide Alarm
Carbon monoxide alarms save lives — but only if they're working. Here's how to test yours and what to do if it's not functioning correctly.
A carbon monoxide (CO) alarm that isn't working offers no protection. Testing takes 30 seconds and should be done monthly. Here's how.
How to test a CO alarm
- Press and hold the test button on the front of the alarm for 5–10 seconds (exact timing varies by model)
- The alarm should sound — a series of beeps or a continuous tone
- Release the button; the alarm should stop sounding
- If the alarm doesn't sound during testing, replace the batteries and test again. If it still doesn't respond, replace the alarm.
How often to test
Monthly testing is recommended. Set a reminder — the first of the month is a good anchor. Also test after any period where the alarm has been disconnected (e.g., during decoration).
When to replace the alarm
Most CO alarms have a lifespan of 5–7 years. The alarm itself will often beep intermittently when the sensor reaches end of life (different from a CO alert, which is a loud continuous alarm). Replace alarms that are more than 7 years old regardless of apparent function.
The legal requirement
Since October 2022, a CO alarm is legally required in every room containing a fixed combustion appliance (boiler, gas fire, log burner). This applies to both owner-occupied and rental properties.
What to do if the alarm activates for real
- Leave the property immediately
- Leave the door open
- Call the National Gas Emergency Service: 0800 111 999
- Do not re-enter until the property has been inspected and cleared
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