Smoke alarm installation, mains-wired and linked through the house.

Interlinked smoke alarms and what Grade D1 means

Interlinked means the alarms are connected, by a wire between them or by radio, so smoke on the landing sets off the alarm in the kitchen and every other one in the house. A fire that starts downstairs at night gets heard in the bedrooms while there's still time to get out.

BS 5839-6 is the code of practice for fire alarms in homes, and it sorts them into grades by how they're powered. Grade D1, which the standard job uses, means each alarm runs off the mains and has a tamper-proof backup battery built in for the alarm's whole life. Grade D2 alarms are mains-powered too, with a backup battery the householder changes. Alarms that run on batteries alone sit in a lower grade.

Radio-linked alarms still need a mains supply at each alarm, but they save running a link cable between floors, which helps in a finished house where lifting floorboards isn't welcome.

Where smoke and heat alarms have to go

Smoke alarms go on the ceiling in the hall and on each landing, the circulation spaces you'd escape through. That's where Approved Document B puts them in new homes, and where the government's guidance for landlords suggests they go too.

Kitchens get a heat alarm, because cooking fumes set off smoke alarms and people end up taking them down. A heat alarm only sounds when the temperature climbs, so it ignores everyday cooking. Bathrooms and toilets usually need nothing, as steam has the same effect on a smoke alarm.

A third storey or an open-plan ground floor changes how many alarms are needed and where they sit, so anything past the standard job gets priced after I've looked round the house.

Testing interlinked alarms at home

Pressing the test button on one interlinked alarm should set off every other alarm in the house, which proves the link as well as the sounder. If one stays quiet, that alarm or its link needs looking at before anything else.

Running a vacuum nozzle over the vents now and then keeps dust out of the smoke chamber. Landlords are advised to keep a record of when the alarms were tested, and the start of a tenancy is the obvious time to do it with the tenant there.

Smoke alarm requirements for landlords in England

Since 1 October 2022, social landlords as well as private ones in England must have a smoke alarm on every storey with living accommodation. Every room with a fixed fuel-burning appliance, such as a boiler or a wood burner, also needs a carbon monoxide alarm. Gas cookers don't count.

Nothing in the regulations says what type of alarm to fit. The government's guidance recommends alarms made to BS 5839-6, and says sealed-for-life batteries are the better choice where alarms run on batteries. Each alarm has to work on the day a new tenancy begins, and a landlord who's told one is faulty has to repair or replace it.

Licensed HMOs follow the conditions the council puts on their licence. Fire safety law also covers guesthouses and the common parts of HMOs, and it can ask more of the electrics in guesthouses and HMOs, such as emergency lighting on the escape route.

Loft conversion smoke alarms and new homes

A loft conversion does need interlinked smoke alarms. Turning a loft into a bedroom puts a new room above the ground storey, and Approved Document B then calls for an alarm system covering the house. The Planning Portal's guidance on loft conversions puts mains-powered, interlinked smoke alarms in the stairway at each level, and Approved Document B wants a battery or capacitor behind each one. Building Control checks for them at sign-off, so it makes sense to plan them with the loft conversion electrics.

New homes follow the same guidance. Approved Document B also says a design, installation and commissioning certificate should be provided for a fire detection and alarm system, and every alarm system I fit comes with a certificate.

Holiday lets and B&Bs with paying guests

Holiday lets and B&Bs on the Yorkshire coast come under fire safety law as business premises, and the Home Office publishes a guide for small places that take paying guests. It expects interlinked smoke and heat alarms that run off the mains with a tamper-proof backup battery, the same Grade D1, with smoke alarms in the hallways, stairs, living rooms and bedrooms, and heat alarms in kitchens.

Sealed long-life battery alarms are accepted there only as a stopgap until a mains system goes in. Whoever runs the let also needs a written fire risk assessment, and in self-catering lets the alarms should be tried at every change of guests.

Replacing battery smoke alarms in your own home

If you own and live in an older house in England, no law makes you fit mains or interlinked alarms. Scotland has different rules, and every home there needs interlinked alarms.

Battery alarms work when they are kept up, but they tend to come down when the battery starts chirping and stay down. Mains alarms with a sealed backup take that job away, and they last until the replace-by date printed on them.

Business premises and larger guesthouses often need a commercial system to BS 5839-1 instead, and I design and install commercial fire alarm systems too.