How to test a carbon monoxide alarm: a home safety check for smoke and CO alarms

Quick checklist

Why test a carbon monoxide alarm

Carbon monoxide is a gas you cannot see, smell or taste. It can come from a faulty boiler, gas fire, cooker, wood burner or other fuel-burning appliance. An alarm is the most reliable way to know. A test takes seconds.

Testing also checks the battery and sound. An alarm that is silent when you press the button is no use in an emergency.

How to test a carbon monoxide alarm, step by step

1. Find every alarm. Smoke alarms are usually on the ceiling. Carbon monoxide alarms may be on a wall or ceiling, depending on the maker.
2. Read the manual or the label. Each maker has its own button, light and sound. Keep the manual, or look the model up on the maker's website.
3. Press and hold the test button. Hold it until the alarm sounds, then let go. It will be loud, so warn others in the home first.
4. Listen and look. A loud, clear sound and a light, if there is one, mean the test passed.
5. If it does not sound, check the battery, replace it if the maker says you can, and test again. If there is still no sound, replace the alarm.
6. Write the date. A note on your calendar or phone makes the next test easy.

How often

Sources disagree. Some say weekly, others monthly. Follow the maker's instructions. Be Ready advises testing smoke alarms monthly, and many makers suggest the same for carbon monoxide alarms. Pick a day you will remember, such as the first Sunday of the month, and test every alarm at once.

What the beeps mean

Alarms make different sounds for different things: a full alarm, a low battery, a fault or the end of the alarm's life. The patterns differ by maker, so we do not list them here. Check your manual. If you have lost it, search for your model on the maker's website. A full alarm is always serious: act first, then read the manual.

Battery or sealed alarms

Some alarms take replaceable batteries. Others are sealed units with a battery meant to last for years, often described as 10-year alarms. Check the label or manual to see which you have. With a replaceable battery, change it when the alarm tells you to or when the maker advises. With a sealed unit, you replace the whole alarm at the end of its life. Do not try to open it.

The replacement date

Look on the back or side for a date, often marked "replace by". Alarms wear out even if they pass a test. If the date has passed, or you cannot find one, plan to buy a new one. When you shop, choose an alarm that says it meets the relevant British Standard. A carbon monoxide alarm (Retailer link coming soon) and a smoke alarm (Retailer link coming soon) cost little compared with the home they protect, but check the current price.

Where to put alarms

The general idea is to have a carbon monoxide alarm in each room with a fuel-burning appliance, such as a boiler or a gas fire, and a smoke alarm on each floor. In Scotland, the law requires every home, owned or rented, to have interlinked smoke and heat alarms and a carbon monoxide alarm wherever there is a fuel-burning appliance or flue. The right height and distance differ by maker and by appliance, so follow the instructions that came with the alarm. If you are unsure, ask a Gas Safe registered engineer when they next visit.

A quick smoke alarm check

Smoke alarms need the same routine, and the test is the same: press the button. While you are there, check:

• The alarm is not covered, painted or hanging loose.
• There is a smoke alarm on every floor of the home.
• Everyone knows the sound and what to do.
• Your exit routes are clear.

A fire blanket in the kitchen can help with a small pan fire, and you may want an fire blanket (Retailer link coming soon) if you cook a lot. A domestic fire extinguisher (Retailer link coming soon) is only worth having if you know how to use it. Your first step in any fire is to get out, stay out and call 999.

If you are renting

Landlords have legal duties about smoke and carbon monoxide alarms, and the rules differ across the UK. If an alarm is missing or you think it is faulty, tell your landlord in writing. Do not remove an alarm or take out its battery to stop the noise. Our guide to preparedness for renters has more.

What to do if your carbon monoxide alarm sounds

Never ignore it. Do this straight away:

1. Open doors and windows to let in fresh air.
2. Turn off the appliance, only if it is safe to do so.
3. Leave the property and stay outside.
4. Call the National Gas Emergency Service on 0800 111 999.
5. Call 999 if anyone feels unwell.
6. Get fresh air and seek medical advice, even if you feel better later.
7. Do not go back in until you have been told it is safe.

Do not try to find or fix the fault yourself. Never carry out DIY work on a gas supply or appliance.

Do this today (free)

1. Press the test button on every smoke and CO alarm.
2. Check the replacement date on each.
3. Write the gas emergency number on paper and keep it in your kit.
4. Set a reminder for next month.

If you have £10, £25 or £50

These are budgets, not quotes. Prices change, so check the current price first.

• About £10: a replacement battery or a basic carbon monoxide alarm for a single room.
• About £25: a smoke alarm and a carbon monoxide alarm together, if you are missing both.
• About £50: extra alarms for each floor, or a fire blanket for the kitchen.

Sources and further reading

• Be ready for emergencies: checklist and household plan
• Health and Safety Executive
• National Gas Emergency Service (National Gas)
• Smoke and carbon monoxide alarms: booklet for landlords (GOV.UK)