Smoke and Carbon Monoxide Alarms That Keep Working Without Mains

Yes, in almost every case. A power cut does not stop a working smoke alarm, because the alarms most UK households have either run on batteries alone or have a backup battery inside. Electric, mains-operated smoke alarms normally have a 9v backup battery in them in case of a power cut¹, and a hard-wired alarm that beeps every minute or so is usually giving a low battery warning, not reacting to the cut itself². Sealed 10-year battery alarms and ordinary battery alarms carry on exactly as before, because they never touched the mains in the first place³.

What a power cut does change is the risk around you. You will be reaching for candles, torches and perhaps a heater or camping stove, and it is dark. That is the moment your alarms must work, so this page sets out which alarms keep working and why, where each type belongs, what standards to look for when you buy, and what that chirping means when the supply comes back. If you are preparing for outages generally, start with our guide to power cuts and what to do when the electricity goes off.

Battery, sealed 10-year, or mains with backup

There are three kinds of smoke alarm in UK homes, and all three keep working in a power cut if they are maintained. The difference is how much looking-after each one needs.

Fire and rescue services in Northern Ireland and elsewhere advise that if you are purchasing a battery alarm, you should consider one with a sealed long life 10-year battery³. The National Fire Chiefs Council's national guidance notes that ten-year sealed battery smoke alarms cost more to buy, but you avoid the cost of replacing batteries every year, while standard battery operated smoke alarms need their batteries replacing every year⁷. The alarms supplied by North Yorkshire Fire and Rescue Service, for example, have 10-year batteries that cannot be removed and come with a 10-year warranty⁸.

Mains alarms are the type most likely to surprise you after a cut. South Wales Fire and Rescue Service explains that electric alarms normally have a 9v backup battery in them in case of a power cut, and that this should be changed every year; a running-out backup battery can make the alarm beep¹. Northern Ireland's fire safety guidance makes the same point: smoke alarms linked to the home mains electrics contain a nine volt backup battery that needs to be changed according to the manufacturer's instructions⁹. So a mains alarm that starts chirping after the supply returns is very often telling you its backup battery is tired, not that the alarm is faulty.

One rule applies to every type: never disconnect or take the batteries out of smoke alarms unless you intend to replace them immediately⁸. An alarm with no battery is the one thing worse than no alarm, because it looks fitted while doing nothing.

Where to fit smoke and heat alarms

The minimum is one smoke alarm on every level of your home, fitted on the ceiling and at least 30cm away from the wall¹⁰. Devon and Somerset Fire and Rescue Service recommend a smoke alarm in your hallway and one at the top of your stairs, and suggest you could also have smoke alarms in bedrooms and other living areas¹¹. nidirect's home fire safety advice adds that it is worth thinking about extra alarms in the most used rooms, such as living rooms and bedrooms¹².

Mounting position matters as much as count. Smoke alarms should always be mounted on the ceiling, near the middle of the room or hall, and at least 30cm (one foot) away from a wall or light¹³. Smoke rises and spreads across a ceiling, so the middle of the ceiling is where an alarm senses it soonest.

Two rooms need a different alarm altogether. Do not fit smoke alarms in kitchens or bathrooms, where smoke or steam could set them off accidentally; install a heat alarm in the kitchen instead¹⁰. Heat alarms are best for kitchens¹⁴ because they respond to the sustained temperature rise of a real fire rather than the fumes of burnt toast or a steamy shower. A heat alarm in the kitchen is also standard advice in homes with telecare-linked detection, where smoke alarms are fitted in all areas where a fire can start, including bedrooms and lounges, and a heat alarm is installed in the kitchen¹⁵.

Interlinking is worth having if you can. Ideally alarms should be hardwired and interlinked, which is a legislative requirement for rented accommodation¹⁶. Some battery or mains alarms can be interlinked so that when one alarm detects a fire they all go off together, giving a warning wherever you are in the home; the fire and rescue service particularly recommends this for people with mobility issues that may prevent or delay escape¹³. Scottish Fire and Rescue Service advice is that all smoke and heat alarms should be ceiling mounted and interlinked¹⁷.

Carbon monoxide alarms: one in every room with a fuel-burning appliance

Carbon monoxide has no smell and no taste, and it kills without warning, which is why the NHS advises you to get one carbon monoxide alarm for each room of your home containing appliances that burn gas, oil, coal or wood⁵. Fire and rescue services say the same: have a carbon monoxide alarm in every room which has appliances that burn fossil fuels⁸, and fit a CO alarm in all rooms containing fuel burning appliances, ensuring the alarm is able to be heard throughout your home¹⁸. Devon and Somerset's carers guidance lists the rooms to cover: all rooms containing solid fuel appliances, any gas appliances or paraffin heaters¹⁹.

That list is longer than many households expect. A CO detector should be fitted in any room where there is a carbon-fuelled appliance, including boilers, fires including open fires, heaters, and stoves or a flue¹⁷. If you use a fireplace, a wood-burning stove, a gas boiler in a cupboard, a paraffin heater during a power cut, or a camping stove indoors in an emergency, each of those rooms needs its own alarm. Our page on carbon monoxide risks when the heating is off covers the dangers of bringing alternative heaters and stoves indoors.

In Northern Ireland the requirement is written into building regulations: carbon monoxide alarms are a mandatory requirement for all homes where a new fossil fuel appliance is installed, following a change to The Building Regulations (Northern Ireland) 2012 that came into operation on 31 October 2012²¹.

Siting a CO alarm: 1 to 3 metres from the appliance

North Wales Fire and Rescue Service's alarm advice sheet gives the siting rules in plain figures. The alarm must be 1 to 3 metres away from the appliance: a minimum of 1000mm and a maximum of 3000mm⁶. If it is mounted on the ceiling, it must be a minimum of 300mm away from the wall⁶. Where alarms are located in sleeping rooms or rooms remote from the appliances, they should be located just below but relatively close to the breathing zone of the occupant, and between the occupant and the appliance⁶.

Do not fit a CO alarm at low level. The Health and Safety Executive for Northern Ireland notes that carbon monoxide is slightly lighter than air, therefore fitting carbon monoxide alarms at low level is not recommended²¹. This is the opposite of a popular myth that CO sinks to the floor, and it is the reason wall-mounting at breathing height or ceiling-mounting is the correct approach.

Standards to look for when you buy

An alarm is only trustworthy if it was built and tested to a recognised standard, and the marks are printed on the alarm or its packaging. Make sure any alarms you buy are marked with a current British Standards or European (CE) safety mark, which shows they are certified as effective²². London Fire Brigade gives the same advice for both smoke and heat alarms²³.

For carbon monoxide alarms the standard to look for is BS EN 50291. Before purchasing a carbon monoxide alarm, always ensure it complies with British Standard EN 50291 and carries a British or European approval mark, such as a CE mark or Kitemark; this is the advice of the Health and Safety Executive²⁴, the Health and Safety Executive for Northern Ireland²¹ and North Yorkshire Fire and Rescue Service⁸. North Wales Fire and Rescue Service is more specific still: for domestic dwellings only use BS EN 50291-1:2010 compliant alarms, and for boats, campers and caravans use BS EN 50291-2:2010 compliant alarms⁶.

For alarms for deaf and hard of hearing people there is a dedicated standard: British Standard BS5446-3:2005 specifies smoke alarm kits for deaf and hard of hearing people, and products made to this standard give deaf people assurance of quality smoke alarms designed to meet their needs²⁵.

Smoke alarms can be purchased from most DIY stores and some supermarkets²⁶, and carbon monoxide alarms are available from DIY and hardware stores²⁰ as well as many retail outlets including online sellers and supermarkets²¹. Wherever you buy, check the standard before you pay, not after.

Testing, batteries and the chirp after a power cut

Test your smoke alarms at least monthly to ensure they are working²⁷. In Northern Ireland the fire safety message is to test weekly⁹, and involving children in the monthly tests is recommended so they know what your smoke alarms sound like when they go off²⁷. Devon and Somerset advise that when you do your smoke alarm testing, you also practise your escape plan with your child, which helps them get used to the sound, stay calm and know exactly what to do²⁸.

Battery care depends on the alarm. If there is a battery, change the battery every year²⁸, unless it is a ten-year alarm, in which case you change nothing until the decade is up¹³. Most smoke alarms need replacing after 10 years: check your warranty and replace your alarm every 10 years¹³.

The chirp that puzzles people most is the one that starts around a power cut. If an alarm beeps every minute or so, this could be a low battery warning, and this can also occur with hard-wired, mains-connected alarms, because there is often a battery backup in case of a power cut². In other words, the cut did not cause the fault; it revealed a backup battery that was already near the end of its year. The fix is the routine one: replace the backup battery, and put the annual change in your calendar so it does not recur¹.

If an alarm was fitted by your fire and rescue service and it is not working correctly, they will come and take a look and replace it if necessary². North Yorkshire Fire and Rescue Service, for example, supplies alarms with a 10-year warranty and gives contact numbers for replacements during that period⁸.

Alarms for people who are deaf, hard of hearing or less mobile

A standard smoke alarm is no use to someone who cannot hear it, especially asleep. If you are deaf or hard of hearing and live alone, or with others who are also deaf or hard of hearing, you can get a smoke alarm that uses a strobe light and vibrating pads that are placed under your pillow at night²⁹. London Fire Brigade's easy-read guidance confirms you can get a special alarm if you are deaf, hard of hearing or have a visual impairment³⁰.

These specialist alarms can save lives: they alert the user to a fire in the home even if they have removed their hearing aid at night³¹. A vibrating pad is placed under a mattress or pillow at night; when smoke is detected, the pad vibrates and the strobe light flashes to alert the sleeper³¹. The Northern Ireland Fire and Rescue Service advises that for anyone with impaired hearing, there are sensory alarms available which include a vibrating pad and flashing light, and to contact your GP to arrange an assessment¹⁶.

For people with limited mobility, an alarm should be fitted where they sleep¹⁶. Interlinked alarms matter here too: because some battery or mains alarms can be interlinked so that when one alarm detects a fire they all go off together, someone with mobility issues gets the warning early wherever the fire starts, giving the most time to escape¹³.

Telecare and monitored detection

For people who may not be able to respond to a smoke alarm, for example due to mobility issues, memory loss or a learning disability, fire and rescue services recommend monitored smoke detection, often through telecare³². Standard telecare usually includes an emergency alarm unit with a red button pendant so help can be requested from a monitoring centre³². Linked smoke detectors are wired or wirelessly interlinked so if one alarm activates, all alarms activate³², and linking fire alarms to telecare limits delays in calling the fire brigade, reducing the likelihood of injury or death occurring as a result of a fire¹⁵.

If the person you care for has telecare fitted, check that it is linked to the smoke alarms³³. Fire and rescue services can fit specialist fire or smoke detection and alarm equipment free of charge for people with impairments that need it, specified through the home safety visit request form³⁴.

Booking a free home fire safety visit

Every fire and rescue service in the UK offers free home fire safety visits, and this is the single most useful thing a household can do short of fitting the alarms itself. Firefighters conduct home fire safety visits to prevent accidental dwelling fires and protect the public from being injured in them¹⁷. Fire and rescue service staff assess fire risk, install fire safety equipment such as smoke alarms, and give potentially life-saving fire safety advice to residents, as the National Fire Chiefs Council's position statement sets out³⁵.

What a visit involves and who gets one varies by service, so check your own:

A visit covers checking smoke alarms are set up correctly, making a fire escape plan, electrics and charging safely, cooking safely, heaters and heating, bedtime checks, and identifying any further support, and may include fitting specialist fire safety equipment where required³⁰. Enhanced visits can also give advice about health and wellbeing, including support on giving up smoking, avoiding falls, keeping your home warm and living with dementia³⁰. British Sign Language and some foreign language translations can be provided during visits if you ask when booking³⁰.

Eligibility is targeted at those who need it most. Services determine eligibility using information gathered from various sources, including personal factors, lifestyle factors and home environment, plus incident data and partner agencies, and criteria may change to manage demand and consider appropriate use of public money³⁰. If you or anyone you live with is a vulnerable person, get in touch and organise a free home fire safety visit²³. You may not need a visit at all: some services will instead give up to date guidance on reducing fire risk and free smoke alarms if required³³.

One household in Devon and Somerset described the outcome plainly: the service gave him equipment that would wake him if there is a fire when he takes his hearing aid out at night³⁰.

Checking the visitor is genuine

Home fire safety visits are free, and no one from a fire and rescue service will ask you for money. If you have any concerns about the identity of someone visiting you, call the number your service publishes: Devon and Somerset Fire and Rescue Service ask residents to ring 0800 05 02 999³⁰. Look up your own service's verification number on its website before the visit so you have it to hand. The same caution applies to callers claiming to be from the electricity network, which we cover in our page on checking a caller from the electricity network is genuine.

Children, alarms and escape plans

Government fire safety advice is blunt on one point: do not assume that everyone has heard the smoke alarm, particularly at night, because some children may not be woken by smoke alarms²⁷. Act quickly and get everyone out as soon as possible²⁷. That makes two habits worth building:

• Get your children involved in testing your smoke alarm and talk to them about what to do if the smoke alarm sounds²⁸
• Make sure children know what your smoke alarms sound like when they go off, by involving them in your monthly tests²⁷
• Practise your escape plan with your child when you test, so they get used to the sound, stay calm and know exactly what to do²⁸

If a child in the household has additional needs, this practice matters even more, as the fire and rescue service recommends it particularly for children with additional needs²⁸. For lighting that children can use safely in an outage, see our guide to emergency lighting at home, and for the wider routine, our page on staying safe in the dark.