Why is my carbon monoxide alarm beeping?

A single chirp every 30-60 seconds almost always means low battery — replace the AA batteries to stop it. Continuous or repeated beeping means the alarm has detected carbon monoxide — leave the building immediately and call 999.

What battery does a carbon monoxide alarm use?

Most battery-powered carbon monoxide alarms use 3 AA batteries. Some models use 2 AA batteries. Check the battery compartment on your specific alarm.

Is it safe to silence a beeping CO alarm?

Only silence a CO alarm if it is making a single intermittent chirp — this means low battery and you can press the silence button and replace the batteries. If the alarm is making a continuous or repeated alarm pattern, do NOT silence it. Leave the building immediately and call 999. Carbon monoxide is odourless and invisible.

⚠️ Continuous alarm sounding?

Leave the building immediately. Do not investigate.
Call emergency services from outside — 999 (UK) or 911 (US).
Carbon monoxide is odourless, colourless and deadly.

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Why is my CO alarm beeping?

Single chirp every 30–60 seconds = low battery.
Replace the AA batteries to stop it.

If your carbon monoxide alarm is making a single intermittent chirp — not a continuous alarm — the battery is almost certainly the cause. Most CO alarms use 3 AA batteries.

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What do the different beeps mean?

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Low battery

Single chirp every 30–60 seconds

Low battery. Replace the AA batteries. This is safe to deal with at your own pace — it is not a CO alert. Replace batteries as soon as possible and never ignore this warning.

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DANGER — Carbon Monoxide

Continuous or repeated alarm pattern

Leave the building immediately. Call emergency services from outside — 999 in the UK, 911 in the US. Do not go back inside until emergency services say it is safe. Carbon monoxide is invisible and odourless — you cannot detect it without an alarm.

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End of life

5 beeps every minute

Many CO alarms beep 5 times per minute to indicate they have reached end of life (typically 7–10 years). Replace the entire unit — not just the battery. The sensors degrade over time and will no longer protect you reliably.

How to replace the batteries

Press and hold the test/silence button for 5–10 seconds to silence the chirping temporarily.
Remove the alarm from the wall or ceiling — usually a twist anticlockwise or a tab to release.
Open the battery compartment and remove all old batteries.
Insert fresh AA batteries — most alarms take 3 AA, some take 2. Check the compartment label.
Press the test button to confirm the alarm is working. You should hear a short alarm sound.

Never permanently remove the batteries from a CO alarm. Carbon monoxide kills silently. An alarm with no battery offers zero protection. Replace the batteries immediately.

Replace CO alarm batteries once a year — set a reminder on the same date each year. Many people do it when the clocks change. Replace the entire alarm every 7–10 years.

Which battery does a CO alarm use?

Most battery-powered carbon monoxide alarms use 3 AA batteries. Some compact models use 2 AA batteries. The battery type and quantity are printed inside the battery compartment.

Popular brands and their batteries: Kidde CO alarms — 3 AA. FireAngel CO alarms — 3 AA. Ei Electronics CO alarms — 3 AA. Nest Protect — 6 AA (battery version).