The dos and don'ts of mains powered smoke alarms and battery alarms

Picture of smoke alarm fixed to the ceiling

Most properties in the UK have battery-operated smoke alarms, but mains powered smoke alarms interlinked between floors are the most reliable method of giving early warning in case of fire and must now be installed in all new homes.

Mains-wired smoke alarms are also required in certain types of alteration and extension work. Mount them in the circulation space at every floor level:

  • In loft conversions
  • When adding new habitable rooms (bedrooms, kitchens, living or dining rooms) above ground floor level
  • When adding a new habitable room at ground floor level that doesn’t have its own exit leading outdoors

Installing new interlinked smoke alarms can be disruptive, so think about the need for detection before you start work. Radio-linked alarms are acceptable; as long as the manufacturer can guarantee the battery back-up will last for 72 hours.

Smoke alarm DOs:

  • Ensure there's at least one alarm on every storey of the dwelling
  • Ensure there's an alarm within 7.5m of the door to every habitable room
  • Provide a heat detector to the kitchen if it's open plan to the escape route
  • Mount them 300mm away from walls and light fittings
  • Ensure the electrical installation of the units meets Part P requirements
  • Provide instructions to the end user

Smoke alarm DON'Ts:

  • Install them above staircases where testing and maintenance is dangerous
  • Site them in places where they can become very hot, cold, or subject to a lot of moisture or fumes (bathrooms, kitchens, garages - use a heat detector if need be)

Remember, there are additional requirements for large houses of two or more storeys where one of those storeys exceeds 200m2, so bear this in mind when working on footballers' mansions! If in any doubt, contact your local authority building control team to discuss.

Further information about fire safety

Also view: How to protect residents from carbon monoxide poisoning


Please Note: Every care was taken to ensure the information was correct at the time of publication. Any written guidance provided does not replace the user’s professional judgement. It is the responsibility of the dutyholder or person carrying out the work to ensure compliance with relevant building regulations or applicable technical standards.

This article was updated on 28 March 2022


Loft space

Submitted 5 years 10 months ago

With so many properties having photo voltaics with the invertors in the roof should there not be a requirement for a smoke alarm in the loft space

Insulation location

Submitted 5 years 10 months ago

Depends on the insulation location as condensation could be a problem (see ADB 1.17)

Multiple ownership

Submitted 5 years 10 months ago

While houses as individuals are regulated what happens with shop fits under flats and older buildings that are joined but have multiple ownership and multiple tenants all working to their own end . Long terraces of shops could be at risk in the same way, one empty or unregulated building in a terrace can distroy many .its time for regulators to pick a simple system and inforce it for all ; unless insurance companies are regulated and the public purse protected.
Would not trust any of the so called experts until they put up some assurance , ie if ex fire officers wish to be seen as the compidient experts lets see their pension funds cover their risk assessments. Ian Malone


Submitted 5 years 10 months ago

Hi we live in a first floor flat does are smoke alarm have to be connected to the downstairs passageway we each have are own down leading into our flats but the passageway is for both of us to use.


Submitted 5 years 10 months ago

Hello there

Generally smoke detectors aren't positioned in the common hallway/stairs in flats as they're often disabled due to false alarms.

John Allen


Submitted 5 years 10 months ago

I have two powered smoke alarms problem is the link cable had only been run in 1.5 2 core and earth is it ok under regulations to power each smoke alarm from two separate lighting roses and just use 1 of the wires in the link cable to link them.

In reply to by julie.mcnamee

(No subject)

Submitted 5 years 10 months ago

Hello there

Thanks for your comment. You'll find guidance about power supplies in sections 1.19 to 1.22 in Approved Document B Volume 1 if it's in a house (here's the link

Or if it's in a flat, in Volume 2 (here's the link

Many thanks,

John Allen, LABC

In reply to by julie.mcnamee

smoke detectors

Submitted 4 years 9 months ago

i would of course suggest the correct wiring being carried out and advise you to replace this cable with 3 core t+e.
until this has been rectified i would suggest that you use the earth of the 2 core cable installed as the interlink for your own safety. smoke detectors are plastic so dont require earthing but obviously you then have a cable with no cpc.....
get it sorted out mate

Webmaster note

Submitted 5 years 10 months ago

All comments posted at an earlier date to this one have been transferred from our old website.

Mains wired smoke alarms

Submitted 5 years 9 months ago

I have two mains wired smoke alarms that were installed in 2002. Batteries have been replaced when indicated by beeps. Both work with the test button. I know they work because putting a steak on a hot griddle pan sets them off even though the lower one is in the hall not the kitchen! They are vacuumed every week to make sure they are clean (if not they go off). Do they need replacing because of time or is what I have heard just a catch all?

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