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Carbon monoxide alarms: where to fit them, how to test them and what the law says

Why you need a carbon monoxide alarm, which rooms need one, where to position it, the legal duties on landlords in England, the symptoms of CO poisoning and what to do if your alarm sounds.

Carbon monoxide (CO) is a poisonous gas produced when fuel doesn't burn properly. The NHS warns that it is colourless and doesn't smell, so you can't tell it's there. An alarm is the only practical way to know. This guide covers which rooms need one, where to put it, how to look after it, and the legal duties for rented homes in England.

Where carbon monoxide comes from

According to the NHS, appliances used for heating and cooking can produce carbon monoxide if they aren't installed properly, are faulty or are poorly maintained. Common sources include:

gas boilers;
gas cookers and clay ovens;
gas or paraffin heaters;
wood, gas and coal fires, including log burners;
portable generators.

Using a barbecue or camping stove indoors, or running a car or lawnmower engine in an enclosed space such as a garage, can also cause a dangerous build-up.

Which rooms need an alarm?

The NHS advises getting a CO alarm for each room of your home containing appliances that burn gas, oil, coal or wood. In most homes that means the room with the boiler, any room with a gas fire or wood burner, and the kitchen if you have a gas hob or oven. If a boiler is in a cupboard off a bedroom or hallway, put the alarm in the room the cupboard opens into.

Where to position it

Always follow the alarm manufacturer's instructions, because designs differ. As general guidance, the government's booklet for landlords and tenants says CO alarms should be positioned at head height, on a wall or shelf, approximately 1 to 3 metres away from a potential source of carbon monoxide. In practice, that means:

not directly above a cooker or boiler, where normal short bursts of combustion gases could cause false alarms;
not in an enclosed cupboard or behind curtains or furniture, where air can't reach it;
not next to a window, door, extractor fan or air vent, where draughts dilute the air;
somewhere you'll hear it, including from bedrooms at night.

Your local fire and rescue service may also give installation advice, and the government's Fire Kills campaign has general home fire safety information.

Choosing an alarm

The NHS recommends an alarm that makes a loud sound if carbon monoxide is present. Check the packaging for the standard it meets and its stated lifespan. Many have a sealed battery that lasts the life of the sensor, so there's no battery to forget about. Avoid cheap "spot" indicators that change colour; they don't wake you up.

Testing and replacing

Test it regularly using the test button, following the manufacturer's recommended frequency.
Replace it at the end of its life. Sensors wear out. Most alarms show an end-of-life warning, often a chirp or a light pattern described in the manual. Write the replacement date on the alarm when you fit it.
Keep it clean. Dust and paint can block the sensor. Don't paint over an alarm.

An alarm is a back-up, not a substitute for maintenance. The NHS advises getting boilers, heaters and cookers serviced regularly by a qualified and registered engineer, keeping rooms well ventilated and keeping chimneys and flues clean. For gas appliances, the engineer must be Gas Safe registered. Our seasonal home maintenance checklist includes a reminder to book the boiler service.

The law for rented homes in England

Since 1 October 2022, under the Smoke and Carbon Monoxide Alarm (England) Regulations 2015, as amended, relevant landlords, including social landlords, must:

make sure a smoke alarm is fitted on each storey with a room used as living accommodation;
make sure a carbon monoxide alarm is fitted in any room used as living accommodation that contains a fixed combustion appliance, other than a gas cooker;
check the alarms work on the day a new tenancy begins;
repair or replace alarms as soon as reasonably practicable after a tenant reports they aren't working.

A "fixed combustion appliance" means a fixed device that burns fuel to generate heat, such as a gas or oil boiler or a log-burning stove. The government's guidance says a purely decorative, non-functioning fireplace wouldn't count. Bathrooms and toilets count as living accommodation under the regulations, and a hall or landing counts as a room.

The regulations don't specify where alarms must be placed; landlords should follow the manufacturer's instructions. Local councils enforce the rules and can impose a fine of up to £5,000 where a landlord fails to comply with a remedial notice.

If you rent and your alarm is missing or faulty, tell your landlord in writing and keep a copy. If nothing happens, contact your local council's private housing team.

Rules differ in Scotland, Wales and Northern Ireland, so check the guidance for your nation if you live there.

Know the symptoms

The NHS lists symptoms of carbon monoxide poisoning including headache, dizziness, feeling or being sick, weakness, tiredness and confusion, chest and muscle pain, shortness of breath and loss of vision. They may come and go, getting worse in an affected room and better when you go outside. If several people in the home, or pets, feel unwell at the same time, take it seriously.

What to do if the alarm sounds

Stop using appliances you think might be producing CO, if you can do so safely.
Get everyone outside into fresh air. Open doors and windows on the way if it's quick to do.
Call the National Gas Helpline on 0800 111 999 if you think a gas appliance is leaking carbon monoxide. The NHS says the line is free and open 24 hours a day.
Get medical advice. Call NHS 111 if you might have symptoms. Call 999 or go to A&E if someone is finding it hard to breathe, has suddenly become confused, has lost consciousness, or has chest or muscle pain. The NHS says not to drive yourself to A&E.
Don't go back in until you've been told it's safe, and don't use the appliance again until a registered engineer has checked it.

Frequently asked questions

Which rooms need a carbon monoxide alarm?

The NHS advises one in each room containing appliances that burn gas, oil, coal or wood.

Where should a carbon monoxide alarm go?

Follow the manufacturer's instructions. Government guidance says, in general, at head height on a wall or shelf, about 1 to 3 metres from a potential source of carbon monoxide.

Do landlords have to fit carbon monoxide alarms?

In England, yes. Since 1 October 2022, relevant landlords must fit one in any room used as living accommodation that contains a fixed combustion appliance other than a gas cooker, check alarms work at the start of a new tenancy, and repair or replace faulty alarms once told.

What are the symptoms of carbon monoxide poisoning?

The NHS lists headache, dizziness, feeling or being sick, weakness, tiredness and confusion, chest and muscle pain, shortness of breath and loss of vision.

What number do I call if I suspect a carbon monoxide leak from a gas appliance?

The free National Gas Helpline on 0800 111 999, open 24 hours a day.

Sources and further reading

Facts and links checked on 21 October 2026. Spotted an error? Tell us and we will correct it.