Glossary · Faults, servicing and gas safety
What is a carbon monoxide alarm?
A carbon monoxide alarm is a small detector that sounds a loud warning when carbon monoxide builds up in a room. The gas has no smell or colour, so people cannot detect it themselves. An alarm gives early warning of a fault but does not stop one, and it does not replace servicing by a Gas Safe registered engineer.
Key points
- HSE strongly recommends alarms, and says to buy one that meets British Standard EN 50291 and carries a British or European approval mark such as a Kitemark.
- The NHS says to fit one in each room of your home that has a gas, oil, coal or wood burning appliance.
- In rented homes in England, landlords must provide a working alarm in any room used as living accommodation that has a fixed combustion appliance, excluding gas cookers.
- Guidance says to fit alarms at head height, about 1 to 3 metres from a potential source, following the maker's instructions.
- An alarm does not replace regular maintenance and safety checks by a Gas Safe registered engineer.
How a carbon monoxide alarm works
Carbon monoxide is colourless, odourless and tasteless, so you cannot tell it is there.[4]Health and Safety Executive, Gas safety - Carbon monoxide awareness frequently asked questions An alarm does that job for you. It detects the gas and makes a loud sound if it is present.[1]NHS, Carbon monoxide poisoning
HSE strongly recommends alarms as one useful precaution that gives advance warning of carbon monoxide in a property. It is clear on the limit, though. Alarms should not be regarded as a replacement for regular maintenance and safety checks by a Gas Safe registered engineer.[2]Health and Safety Executive, Domestic gas: frequently asked questions The alarm tells you something is wrong. A gas safety check or boiler service is what helps stop it going wrong in the first place.
Choosing and fitting one
Before you buy, check that the alarm meets British Standard EN 50291 and carries a British or European approval mark, such as a Kitemark. HSE says it should be installed and maintained following the manufacturer’s instructions.[2]Health and Safety Executive, Domestic gas: frequently asked questions
| Question | Guidance |
|---|---|
| How many? | The NHS says one for each room containing a gas, oil, coal or wood burning appliance |
| Where in the room? | 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 |
| Which type? | The rules do not say. Mains powered or battery powered are both allowed. Sealed-for-life batteries are described as the better battery option |
| Testing | Follow the manufacturer’s instructions for testing, and test regularly |
The “where” and “which type” rows come from guidance written for landlords and tenants in England. It adds that the regulations do not stipulate a position, and that you should follow the manufacturer’s instructions.[3]Ministry of Housing, Communities and Local Government, Smoke and Carbon Monoxide Alarm (Amendment) Regulations 2022: guidance for landlords and tenants
What landlords in England must do
The government guidance, last updated in July 2022, says that from 1 October 2022 landlords of rented homes in England must equip a carbon monoxide alarm in any room used as living accommodation that contains a fixed combustion appliance, excluding gas cookers. They must also repair or replace alarms once they are told one is faulty. Local authorities enforce this and can impose a fine of up to £5,000 if a landlord fails to comply with a remedial notice.[3]Ministry of Housing, Communities and Local Government, Smoke and Carbon Monoxide Alarm (Amendment) Regulations 2022: guidance for landlords and tenants
For a new tenancy, landlords must check that each required alarm works on the day the tenancy begins.[3]Ministry of Housing, Communities and Local Government, Smoke and Carbon Monoxide Alarm (Amendment) Regulations 2022: guidance for landlords and tenants Tenants who find an alarm not working are advised to replace the batteries first, and to tell the landlord if it still does not work.[3]Ministry of Housing, Communities and Local Government, Smoke and Carbon Monoxide Alarm (Amendment) Regulations 2022: guidance for landlords and tenants The rules do not apply to every tenancy. Shared accommodation with a landlord or their family, long leases, hotels and care homes are among those excluded.[3]Ministry of Housing, Communities and Local Government, Smoke and Carbon Monoxide Alarm (Amendment) Regulations 2022: guidance for landlords and tenants
Example
Imran rents out a terraced house in Bradford. The gas boiler is in the kitchen and there is a gas fire in the lounge. Under the 2022 rules he equips an alarm in the living room with the fire. He also puts one in the kitchen as the NHS advises for any room with a boiler, and he tests both on the day the new tenant moves in. When the tenant reports that the kitchen alarm is beeping, he replaces it.
What people get wrong
The most common mistake is to treat the alarm as proof the appliance is safe. A silent alarm does not mean a boiler is working properly. It means no carbon monoxide has reached that detector. HSE says alarms are not a replacement for regular maintenance and safety checks.
Another mistake is fitting the wrong product or in the wrong place. Buy one marked EN 50291 and follow the maker’s instructions. If you have no alarm, you can still book the checks that matter: a boiler service with a Gas Safe registered engineer.
The bottom line
A carbon monoxide alarm is an early warning for a gas you cannot sense. Buy one marked EN 50291, fit it where the maker and the NHS advise, and test it. If you rent a home out in England, the law requires one in rooms with a fixed combustion appliance. Whatever the alarm says, keep appliances serviced by a Gas Safe registered engineer.
Common questions
Do I legally need a carbon monoxide alarm?
If you rent your home out in England, yes. Landlords must equip a working alarm in any room used as living accommodation that has a fixed combustion appliance, excluding gas cookers. Owner-occupiers are not covered by that rule, but HSE strongly recommends one.
Where should I put a carbon monoxide alarm?
The NHS says one in each room with a fuel-burning appliance. Government guidance says to follow the maker's instructions and, in general, to fit it at head height on a wall or shelf, about 1 to 3 metres from a possible source.
Does a carbon monoxide alarm replace a boiler service?
No. HSE says alarms should not be regarded as a replacement for regular maintenance and safety checks by a Gas Safe registered engineer. The alarm warns you. The service helps prevent the fault.
What should I do if my alarm goes off?
HSE says to call the National Gas Emergency Service on 0800 111 999, switch off the appliance, shut off the gas at the meter and open all doors and windows. The NHS says to go outside and get medical advice.
Sources
We cite the original source for every figure: government, regulators, standards bodies and manufacturers' own documents. Each one shows the date we last checked it.
- NHS. Carbon monoxide poisoning. Checked 11 November 2026. ↩
- Health and Safety Executive. Domestic gas: frequently asked questions. Checked 11 November 2026. ↩
- Ministry of Housing, Communities and Local Government. Smoke and Carbon Monoxide Alarm (Amendment) Regulations 2022: guidance for landlords and tenants. Checked 11 November 2026. ↩
- Health and Safety Executive. Gas safety - Carbon monoxide awareness frequently asked questions. Checked 11 November 2026. ↩