Battery or Mains Smoke Alarms: Which to Fit and How to Keep Them Working

Either type protects your home. A battery alarm is the simplest to fit yourself, and a mains-wired alarm runs from your household electricity with a back-up battery for power cuts. What matters most is that you have working alarms, that you test them weekly, and that you know when their batteries and the units themselves need replacing.

If you are choosing now, the official advice leans towards a sealed ten-year battery alarm or a mains-wired unit with a back-up battery. Ten-year sealed battery smoke alarms are described as the best option by Lincolnshire Fire and Rescue, because you save on the cost of replacing batteries¹. Mains-powered alarms need a qualified electrician to install them, but they have a back-up battery in case of a power cut².

Whichever you pick, look for the British Standard Kitemark symbol, and for carbon monoxide alarms the EN50291 mark¹. Then keep the alarm in working order: test it weekly, change a standard battery every year, and replace the whole unit when it reaches the end of its life.

Battery or mains: either type protects your home

The first thing to understand is that the choice is not between safe and unsafe. Mains-wired alarms use the same technology as battery-operated detectors and have the same shelf life⁶. What differs is how they are powered, who can fit them, and what maintenance they need from you.

A battery alarm is self-contained. You can buy one, screw it to the ceiling and be protected the same day. A mains alarm draws power from your home's wiring, so it needs a qualified electrician to install it, and it carries a back-up battery so it keeps working if the power fails². That back-up is the part that needs your attention over the years.

For rented homes, the official guidance is specific. Where battery powered alarms are selected, alarms with sealed for life batteries rather than alarms with replaceable batteries are the better option⁷. Ideally alarms should be hardwired and interlinked, which is a legislative requirement for rented accommodation⁸. If you rent, ask your landlord which type is fitted and who is responsible for testing and replacing it.

Sealed 10-year battery alarms: no yearly battery change

A sealed ten-year alarm is the low-maintenance option. You can buy alarms fitted with sealed 10 year batteries⁵, and the fire service's own units often use them: the alarms that Greater Manchester Fire and Rescue Service fits have a ten-year sealed battery which does not need to be changed³. North Yorkshire Fire and Rescue Service says the alarms it supplies have 10-year batteries and cannot be removed¹⁰.

The trade-off is that the alarm is not repairable. You can buy alarms with ten-year batteries, which provide peace of mind, but have to be replaced in their entirety when the battery eventually dies⁴. Scottish guidance describes long-life lithium batteries which can last up to 10 years¹¹. If you have a ten year alarm, or a mains connected alarm, they will need to be replaced every ten years, and the date can usually be found on the alarm itself¹².

A sealed compartment also has a safety benefit. Buying an alarm with a sealed battery compartment will help to prevent tampering or removal of the battery³. That matters in shared or rented homes, and in any household where someone might be tempted to silence an alarm by taking its battery out.

Standard battery alarms need new batteries every year

A standard battery alarm is a simple way to add cover, but it asks something of you every year. In a standard smoke alarm, the battery will need to be replaced every 12 months⁵. If any of your smoke alarms have a one-year battery, you must change them every year¹³. Basic smoke alarms run off nine volt batteries, and these should be replaced on a regular basis⁴.

The rule is the same across the UK's fire services. Change the battery once a year unless it is a ten-year alarm¹⁴. Replace the batteries every year if the alarm has removable batteries¹⁰. You need to replace the battery once a year or when it beeps regularly, whichever is sooner¹². Change the battery every year even if it is still working¹⁵.

A few habits make this easier:

• Pick a fixed date, such as when the clocks change, and change every battery alarm then.
• Only take out the battery when you need to replace it¹².
• Never disconnect or take the batteries out of your alarm if it goes off by mistake¹. Silence it properly and find out why it sounded.
• Keep a spare battery of the right size in the house so a chirping alarm is fixed the same day.

If an alarm keeps beeping after a fresh battery, do not ignore it. Treat it as a fault and deal with it, rather than removing the battery and leaving the alarm dead.

Mains-wired alarms need an electrician and a back-up battery

A mains alarm is wired into your home's electricity, so it is not a DIY job. Mains alarms need to be installed by a qualified electrician⁵, and alarms hard wired to the mains must be fitted by a qualified electrician¹¹. The reason is simple: the work involves your fixed wiring, and a poor connection is a fire risk in itself.

The back-up battery is what keeps the alarm alive in a power cut. Mains-powered alarms are powered by your home power supply and have a back-up battery in case of a power cut². South Wales Fire and Rescue Service notes that electric alarms normally have a 9v back up battery in them in case you have a power cut⁹. Northern Ireland's guidance says smoke alarms linked to home mains electrics contain a nine volt back up battery that needs to be changed according to the manufacturer's instructions¹⁶.

That back-up does not last forever. Many hard-wired smoke alarms also have a back up battery that will need to be replaced when they fail, and signs of this include your alarm making frequent little beeps¹⁷. Change the back up battery every year; a running out battery can make the alarm beep⁹. If the alarm still beeps after the battery is changed, contact a qualified electrician for advice and to check your electrical supply⁹.

Hard-wired smoke alarms should be replaced as per the manufacturer's guidelines, and tested weekly¹⁸. If there is a problem with an alarm that is hard wired to mains electric, contact an electrician, or if in rented accommodation contact your landlord for further advice¹⁹.

Interlinked alarms: radio-linked so one sounds them all

An interlinked system is the single biggest improvement most households can make after fitting alarms at all. 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 home²⁰. Interlinked alarms are when one alarm is triggered all the alarms will go off simultaneously²¹.

The linking can be wired or wireless. Linked smoke detectors are wired or wirelessly interlinked so if one alarm activates, all alarms activate²². Scottish guidance explains that both types of alarm are interlinked by radio frequency and do not need WiFi²¹. That last point matters: a radio-linked system keeps working when your broadband or power does not.

Interlinking is especially valuable in three situations:

• Larger homes. Interconnecting or linking alarms are useful in larger properties and for people who are D/deaf or hard of hearing⁴.
• Anyone who might not hear a single alarm. 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, which helps people with mobility issues that may prevent or delay escape¹⁴.
• Households with a vulnerable person. Make sure alarms are interlinked so that when one alarm detects a fire they all go off together, giving the person early warning²².

If you already have alarms, you may be able to add linking rather than replace everything. Some systems can connect to a telecare, carecall or lifeline service²³, and a radio smoke detector not only raises an audible alarm within the home but provides additional protection by raising an instant alarm call to the monitoring centre²⁴. Ask the maker whether your model accepts a module before buying one, and check that any new unit is compatible with what you have.

Which rooms need an alarm: an LD1 system for fullest cover

Where alarms go matters as much as which type you buy. The fullest cover is an LD1 system, which places detection in every room where a fire could start, including living rooms and bedrooms as well as the hallway and landing. Most homes have less than this, and the fire services' baseline advice is to fit at least one alarm on every level of the home and in the rooms where fires most often start.

At minimum, one smoke alarm should be installed in the room most frequently used for general daytime living purposes¹¹. That is usually the living room, and it is the room where a fire is most likely to begin unnoticed while people are elsewhere. Add alarms in hallways and landings so you hear them at night, and consider heat alarms in kitchens and garages where smoke alarms would cause false alarms.

For a fuller system, think room by room:

• Living room: a smoke alarm, as the main daytime room²⁵.
• Hallway and landing: smoke alarms so a fire downstairs wakes you.
• Bedrooms: smoke alarms, especially where people sleep with doors closed.
• Kitchen: a heat alarm rather than a smoke alarm, to avoid false alarms from cooking.
• Near a chimney or solid fuel appliance: follow the appliance maker's advice, and fit a carbon monoxide alarm as well.

If you are unsure how many alarms your home needs, a room-by-room plan is the place to start. Our guide to how many smoke alarms a house or flat needs sets out the options, and where to fit smoke alarms covers positions on ceilings and walls.

Recalls and safety notices for alarms and detectors

Alarms are safety equipment, so a faulty one is serious. Buy only alarms marked with a current British Standards or European (CE) safety mark, which shows they meet the relevant standard²⁰. For smoke alarms, look out for the British Standard Kitemark and Loss Prevention Certification Board (LPCB) symbols, which show the alarm is approved and safe¹. For carbon monoxide alarms, only buy alarms that have been certified to British Standard EN50291 and have the British or European approval mark, such as the Kitemark¹.

Recalls do happen, and they are worth watching for. Check the batch and model of any alarm you already own against the maker's own safety notices, and follow the recall instructions if yours is affected. When you buy, make sure any alarms are marked with a current British Standards or European (CE) safety mark²⁶. If an alarm starts to chirp, replace your alarm or its battery immediately, and certainly within seven days, as your alarm may not have enough power to warn you of a real fire after this time²⁷.

If you are buying a combined unit, be clear what it detects. A combined smoke and carbon monoxide alarm is not the same as a heat detector, and packaging errors have caused confusion. Our guide to combined or separate alarms explains the difference, and how to check if an electrical product has been recalled covers the general process.

Getting help with choosing, fitting and guarantees

You do not have to work this out alone. Fire and rescue services across the UK offer home safety visits, and many fit free smoke alarms while they are there. The alarms they supply usually have sealed ten-year batteries: the alarms provided by Mid and West Wales Fire and Rescue Service have a 10-year battery life²⁸, and the alarms Greater Manchester Fire and Rescue Service fits have a ten-year sealed battery which does not need to be changed³. Contact your local fire and rescue service to ask what is available where you live.

If you rent, your landlord has duties too. Ideally alarms should be hardwired and interlinked, which is a legislative requirement for rented accommodation⁸. Ask your landlord which alarms are fitted, when they were last tested, and who replaces the back-up battery in a mains unit.

For alarms bought yourself, keep the receipt and guarantee. If an alarm fitted by a fire service is still covered by its guarantee, the maker can help: FireAngel, for example, asks customers to call freephone 0800 141 2561 for support¹⁹. Buying an alarm with a sealed battery compartment will help to prevent tampering or removal of the battery³, which is worth considering in a shared home.

Smoke alarms can be purchased at DIY stores, hardware and electrical shops, and at some supermarkets²⁷. Wherever you buy, check the marks before you pay, and check the replacement date on the unit.

If someone in your household is deaf or hard of hearing, specialised alarms are available: mains-powered smoke alarms with back-up batteries, and vibrating pads and flashing lights that warn people who cannot hear well²¹. Our guide to smoke and CO alarms for deaf and hard of hearing people explains the options, and extra help in an emergency covers support for older, disabled and medically dependent households.