Life safety systems
Residential fire detection — grades, categories, landlord duties and design
Domestic fire detection is what wakes a sleeping household in time to get out. In the UK it is designed to BS 5839-6:2019+A1:2020, expected by Approved Document B in new work, required in rented homes by the Smoke and Carbon Monoxide Alarm (England) Regulations 2015 as amended in 2022, and wired under BS 7671:2018+A4:2026.
This page covers houses, flats, private rented homes, social housing and HMOs. It does not cover commercial or non-domestic premises, which fall under BS 5839-1 and the Regulatory Reform (Fire Safety) Order 2005. Below the guidance there is an interactive designer that produces a room-by-room device schedule and a downloadable A4 PDF design record.
Why it exists
Most fatal house fires happen at night, and it is the smoke that kills long before the flames arrive. Interlinked detection buys the two or three minutes a household needs to wake, get everyone onto the stairs and out of the front door.
What it is not
A single battery alarm screwed to a hall ceiling in 2011 is not a fire detection system. Nor is a carbon monoxide alarm a fire detector — CO detection is a separate duty covering fuel-burning appliances, and one does not substitute for the other.
Who is responsible
In an owner-occupied home, the householder. In a rented home, the landlord must fit the alarms, check they work on the first day of a new tenancy and repair or replace faulty units once told about them; the tenant should test them weekly and report failures.
Grades — how the system is powered
BS 5839-6 splits domestic systems into grades by the type of equipment and its power supply. The grade answers “what kind of system is it?”; the category answers “how much of the house does it cover?”
Grade A
A full fire detection and alarm system with separate detectors, sounders, a control and indicating panel and a standby supply, designed and installed to BS 5839-1 (other than the detection category, which follows BS 5839-6). Used in larger HMOs, bedsit accommodation, sheltered schemes and very large dwellings.
Grade C
Separate detectors and sounders powered from the mains, with a central standby supply and some form of control equipment. Common in sheltered housing and where alarms need to link to a warden call or telecare system.
Grade D1
One or more mains-powered smoke or heat alarms, each with an integral tamper-proof back-up supply — a sealed lithium cell designed to last the life of the alarm, typically ten years. This is the grade to specify for rented homes and new work; there is no battery for anyone to remove.
Grade D2
As D1 but with a user-replaceable back-up battery. Still compliant in many situations, but the battery can be taken out, which is exactly what happens in practice when an alarm nuisance-sounds.
Grade F1
Battery-only alarms with a tamper-proof battery designed to last the life of the alarm. Acceptable only in limited circumstances in existing owner-occupied homes where mains alarms cannot reasonably be installed.
Grade F2
Battery-only alarms with a user-replaceable battery. The weakest arrangement in the standard and not appropriate for rented accommodation.
Categories — how much is covered
LD1
all circulation spaces and all rooms and areas, except bathrooms and shower rooms
LD2
circulation spaces plus rooms of higher fire risk (kitchen and principal habitable room)
LD3
circulation spaces forming the escape route only
Categories beginning PD (property protection) also exist in the standard, but LD (life protection) is what applies to homes and rented accommodation.
Typical recommendation by property
| Property | Grade | Category |
|---|---|---|
| Existing owner-occupied home | D1 (F1 minimum) | LD3, LD2 preferred |
| New build / material alteration | D1 | LD3 minimum, LD2 recommended |
| Loft conversion adding a storey | D1 | LD2 |
| Private rented single household | D1 | LD2 |
| Social housing | D1 | LD2 |
| Shared house up to 2 storeys | D1 | LD2 |
| HMO, 3+ storeys or bedsits | A | LD2 (LD1 in letting rooms) |
| Sheltered / supported housing | A or C, linked to warden call | LD2, LD1 where escape is slow |
Grade and category recommendations are taken from BS 5839-6:2019+A1:2020. The legal minimum in the rented sector is lower than the recommendation — meeting only the minimum can still be judged a hazard under the HHSRS.
Sensor types and what goes where
Optical (photoelectric) smoke alarm
Detects the larger smoke particles produced by slow, smouldering fires — bedding, upholstery, overheating cables. The default smoke alarm for circulation spaces and bedrooms in UK homes.
Heat alarm
Responds to a rate of rise in temperature or a fixed threshold, typically 58 °C. It ignores steam, smoke and cooking fumes, which is why the kitchen, utility room and integral garage get a heat alarm and never a smoke alarm.
Multi-sensor alarm
Combines an optical smoke chamber with a thermistor and processes both signals together. It reacts faster to a real fire while rejecting toast and shower steam, so it is well suited to halls next to kitchens and to open-plan living areas.
Ionisation alarm (legacy)
Contains a small radioactive source and responds quickly to fast flaming fires but is prone to cooking nuisance alarms. Largely superseded in the UK by optical and multi-sensor units — treat any you find as due for replacement.
Carbon monoxide alarm
An electrochemical sensor to BS EN 50291-1. Carbon monoxide is not a fire product and a CO alarm is not a fire detector — it is a separate legal requirement wherever there is a fixed combustion appliance.
Accessible / assistive alarms
Deaf and hard-of-hearing kits add a pad shaker under the pillow and a high-intensity strobe, triggered by the interlinked alarm system. Worth specifying wherever an occupant may not hear a standard 85 dB sounder.
Siting rules
- • Smoke and heat alarms are ceiling mounted, as close as practicable to the centre of the room.
- • Keep at least 300 mm between the alarm and any wall, light fitting or decorative object.
- • Wall mounting is a last resort — the sensor must sit between 150 mm and 300 mm below the ceiling.
- • In a circulation space, no point should be more than 7.5 m from the nearest smoke alarm.
- • Site an alarm within 3 m of every bedroom door, measured to the door itself.
- • Never fit a smoke alarm in a kitchen, bathroom, shower room or garage — use a heat alarm where detection is needed.
- • Avoid positions above heaters, air conditioning outlets, extract fans or in the direct path of a ceiling fan.
- • Avoid very hot or very cold spaces outside the manufacturer's stated operating temperature range.
- • On a sloping ceiling, mount within 600 mm vertically of the highest point, but not in the apex itself where a dead air space can form.
- • Carbon monoxide alarms go in the same room as the appliance, 1 m to 3 m horizontally from it, at head height or as directed by the manufacturer — not tucked behind the boiler.
- • Do not fit a CO alarm inside an enclosed boiler cupboard, in a dead air space, or directly above a sink.
- • Alarms must be readily accessible for testing, cleaning and eventual replacement without needing a tower scaffold.
Interlinking and supply
Every alarm in a dwelling must operate together. There are two ways to achieve it:
- Hard-wired interconnect — a three-core-and-earth cable between alarm bases carrying the interconnect signal. Best on new work and rewires where the cable can be run without damage.
- Radio interlink — each alarm is still mains powered but the signal is sent by a radio module, house-coded to the property. The practical choice in a finished home, and the standard treats it as equivalent.
Supply the alarms from a regularly used lighting circuit or a dedicated, clearly labelled way at the consumer unit. Label it so nobody switches it off “because nothing seems to be on it”. Cable support must be non-combustible in line with Regulation 521.10.202 of BS 7671 so the wiring cannot fall in a fire.
Rental properties — the legal duty
The Smoke and Carbon Monoxide Alarm (England) Regulations 2015, amended with effect from 1 October 2022, apply to private rented and social housing in England. Wales, Scotland and Northern Ireland have their own, in places stricter, requirements.
The landlord must
- • Fit at least one smoke alarm on every storey used as living accommodation.
- • Fit a carbon monoxide alarm in every room used as living accommodation that contains a fixed combustion appliance — gas boiler, oil boiler, wood burner, open fire — other than a gas cooker.
- • Check every alarm is in working order on the first day of each new tenancy.
- • Repair or replace a faulty alarm as soon as reasonably practicable after being told it is not working.
- • Keep evidence — dated check records, photographs, the inventory and the tenant's signature.
- • Review the arrangement whenever a new appliance is installed or the layout changes.
Failure can result in a remedial notice from the local authority and a civil penalty of up to £5,000.
The tenant should
- • Test every alarm weekly with the test button and report any that do not sound.
- • Never remove an alarm, cover it, or take out a battery to stop it sounding.
- • Report a bleeping or flashing fault alarm straight away rather than living with it.
- • Keep alarms free from dust, paint and cobwebs and never paint over one.
- • Report anything that causes repeated nuisance alarms so the sensor type or position can be changed.
Under the Homes (Fitness for Human Habitation) Act 2018 a tenant can take a landlord to the county court directly where a home is unfit, and inadequate fire detection is one of the matters the court will look at.
Wales
The Renting Homes (Wales) Act 2016 and the Fitness for Human Habitation Regulations 2022 require mains-powered interlinked smoke alarms on every storey and a CO alarm in every room with a gas, oil or solid-fuel appliance, in every occupation contract.
Scotland
Since February 2022 every home, regardless of tenure, must have interlinked alarms: one smoke alarm in the most frequently used room, one in every circulation space on each storey, a heat alarm in the kitchen, and a CO alarm where there is a fuel-burning appliance.
Northern Ireland
Detection follows Technical Booklet E of the Building Regulations (Northern Ireland) and BS 5839-6, with mains-powered interlinked alarms expected in new work and in HMOs licensed by the local council.
Testing, maintenance and end of life
Weekly
Press and hold the test button on one alarm until it sounds, and check every other alarm in the interlinked set also sounds. This is the occupier's job and takes under a minute.
Every tenancy change
The landlord or their agent must check every alarm on the first day of the new tenancy and record the result. A dated photograph in the inventory is the simplest evidence.
Annually
Clean each alarm in line with the manufacturer's instructions, replace any user-replaceable battery, confirm interlink operation across the whole property and check nothing has been added to the property that changes the design.
Ten years
Sensors degrade. Replace every alarm by the expiry date marked on the unit — typically ten years from manufacture, not from installation — and replace the whole interlinked set together.
Grade A systems
Where a Grade A system serves a larger HMO or a sheltered scheme, the servicing regime follows BS 5839-1 instead: a weekly test of a different call point or detector in rotation, a periodic inspection and service at intervals not exceeding six months by a competent person, and a site log book kept up to date and available for inspection.
Good practice on site
- Specify Grade D1 sealed-battery alarms in any property you do not live in — a removable battery will be removed.
- Interlink everything. A single alarm at the far end of a landing does not wake a sleeping household behind a closed door.
- Use a multi-sensor in the hall where the kitchen opens onto it, and a heat alarm in the kitchen itself — that single decision prevents most nuisance alarms.
- Take the supply from a regularly used lighting circuit or a dedicated way, clearly labelled, so it is obvious the circuit must not be left switched off.
- Do not fit an alarm to a circuit protected by an RCD that also serves sockets used for gardening tools — a nuisance trip must not disable the detection.
- House-code radio-interlinked alarms on the day of install, and record the code on the certificate so the next device can be added easily.
- Write the install date on the alarm and record the ten-year replacement date on the certificate and in the tenant's handbook.
- Hand over the BS 5839-6 design, installation, commissioning and acceptance certificates — not just a verbal 'they all went off'.
- Photograph each alarm in position during commissioning; it is the cheapest evidence you will ever collect.
- Where an occupant is deaf or hard of hearing, specify a pad shaker and strobe kit rather than assuming the standard sounder is enough.
- Never blank off, bag over or isolate an alarm to stop it sounding during dusty work — remove it, cap the base safely, and refit and test the same day.
- Replace the whole set at end of life. Mixing a new alarm into a ten-year-old interlinked set gives you a system that is only as reliable as its oldest unit.
Manufacturer guidance and design notes — Aico
Paul specifies Aico for domestic detection. Their technical library is free, kept current with the standards, and is the reference used alongside BS 5839-6 on site. Links open in a new tab.
Aico (Ei Electronics) is the UK market leader in domestic mains-powered interlinked alarms. Everything below is published free on their site.
The starting point for design and installation notes — siting, wiring, house coding, commissioning, maintenance and fault finding.
Room-by-room siting notes with the 300 mm rule, the 7.5 m and 3 m circulation distances, sloping ceilings and the positions to avoid.
Which sensor goes in which room and why: optical, heat, multi-sensor and the reasoning behind avoiding smoke alarms in kitchens.
Wiring diagrams for the interconnect between mains alarms, including where the interconnect core must and must not go.
How to house-code a radio-interlinked system so that neighbouring properties do not trigger each other, and how to add a device later.
The commissioning routine and the paperwork that should be handed over, including the BS 5839-6 certificate set.
Cleaning intervals, what causes false alarms, and how to keep an installed system reliable across its ten-year life.
Plain-English summaries of BS 5839-6:2019, Approved Document J, the England amendment regulations, the Welsh and Scottish requirements and Awaab's Law.
Aico's own breakdown of the grades and categories and what changed in the 2019 edition and its 2020 amendment.
Interactive product selector that returns a suggested alarm mix for a property type. Useful as a cross-check against the design produced below.
How the radio interlink works, its range, and when it is the right answer instead of pulling an interconnect cable through a finished ceiling.
Reading the alarm's own event data through the sounder to diagnose why it went off, which settles most nuisance-alarm arguments with a tenant.
Free manufacturer training on BS 5839-6 design and installation for electricians, with a City & Guilds assured route.
Other useful manufacturers and bodies
Aico's parent group — the wider technical library and product data sheets.
UK manufacturer of mains and sealed-battery smoke, heat and CO alarms with connected-home options.
Independent charity guidance on home fire safety, alarm testing and product recalls.
Manufacturer instructions always take precedence over any general guidance on this page. Where the two differ, follow the instructions supplied with the alarm.
Standards, legislation and free downloads
The core rented-sector duty: at least one smoke alarm on every storey used as living accommodation, and a carbon monoxide alarm in every room used as living accommodation containing a fixed combustion appliance. Free to read in full on legislation.gov.uk.
Extended the duties to social housing from 1 October 2022, added CO alarms for all fixed combustion appliances other than gas cookers, and required landlords to repair or replace a faulty alarm as soon as reasonably practicable once informed.
The explanatory booklet published by the Department for Levelling Up, Housing and Communities setting out exactly what a landlord must fit, test and record. Downloadable at no cost.
Sets the Building Regulations expectation for new dwellings, material alterations and loft conversions in England: mains-powered interlinked alarms with a standby supply, to a minimum of Grade D1 Category LD3. Free download from GOV.UK.
Requires a carbon monoxide alarm to BS EN 50291-1 to be fitted when a fixed combustion appliance (other than a gas cooker) is installed, and sets the siting rules for it.
Code of practice for the design, installation, commissioning and maintenance of fire detection and fire alarm systems in domestic premises. The grades, categories, siting distances and certification all come from here. Purchase from BSI.
The non-domestic system standard, referenced by BS 5839-6 whenever a Grade A system is specified — panel, zoning, cabling, commissioning and servicing. Purchase from BSI.
Product standard and siting code for electrical carbon monoxide detection apparatus in domestic premises. Any CO alarm fitted must be marked to BS EN 50291-1 with an audible alarm.
Fire (hazard 24) is scored under the Housing Health and Safety Rating System. A dwelling with only a token single alarm can still be served with an improvement notice even where the 2015 Regulations are technically met.
Lets a tenant take direct action in the county court where a home is unfit, and inadequate fire detection is one of the matters the court will consider.
The wiring itself: alarm supply circuits, cable selection and support (Regulation 521.10.202), segregation, RCD protection and the requirement that the supply is not readily switched off in error.
Legislation and the Approved Documents are free to download from legislation.gov.uk and GOV.UK. British Standards are copyright documents and must be purchased from BSI — the links go to the publisher, never to unlicensed copies.
Design tool
Domestic fire detection designer & PDF
Set the property type, add each room, and the tool returns the BS 5839-6 grade and category, the sensor type for every room, the carbon monoxide requirement and a full A4 PDF design record with siting notes and a sign-off block. Everything runs in your browser — nothing is uploaded.
Property details
Recommended system
Grade
Grade D1
Category
LD2
Fire alarms
4
CO alarms
1
Mains-powered alarms, each with an integral tamper-proof back-up battery designed to last the life of the alarm, all interlinked.
The Smoke and Carbon Monoxide Alarm (England) Regulations 2015 (as amended 2022) set the legal floor of one smoke alarm per storey. BS 5839-6 recommends Grade D1 Category LD2 for private rented single-household homes, and the HHSRS assessment under the Housing Act 2004 is judged against that recommendation.
- • The legal minimum is a single alarm per storey, but the recognised standard of good practice is interlinked Grade D1 LD2 — meeting only the minimum can still score a hazard under the HHSRS.
- • All alarms must be interlinked — hard wired on a dedicated interconnect core or by radio interlink — so one alarm sounding raises the alarm throughout the home.
Rooms
Fire device
Multi-sensor (optical + heat) alarm
CO alarm
Not required
Ceiling mounted, at least 300 mm from any wall or light fitting, and within 7.5 m of the door to any habitable room. A multi-sensor suits halls next to a kitchen because it resists cooking aerosols.
Fire device
Multi-sensor (optical + heat) alarm
CO alarm
Not required
Ceiling mounted near the centre of the room. A multi-sensor is preferred where an open fire, wood burner or drying laundry causes nuisance alarms.
Fire device
Heat alarm
CO alarm
Required — BS EN 50291-1
Heat alarm only — never a smoke alarm. Ceiling mounted near the centre, at least 300 mm from walls and not directly above the hob, oven or kettle.
Fire device
Optical / photoelectric smoke alarm
CO alarm
Not required
One alarm per landing on the escape route, ceiling mounted at the head of the stairs, at least 300 mm from walls and light fittings.
Fire device
No fire detector required
Outside Category LD2 — included if you upgrade the category.
CO alarm
Not required
Ceiling mounted near the centre of the room, at least 300 mm from walls, light fittings and the path of a ceiling fan.
Fire device
No fire detector required
Outside Category LD2 — included if you upgrade the category.
CO alarm
Not required
Ceiling mounted near the centre of the room, at least 300 mm from walls, light fittings and the path of a ceiling fan.
Fire device
No fire detector required
CO alarm
Not required
No fire detector. Steam and humidity cause persistent false alarms — this room is excluded even in Category LD1.
Grade D1 · Category LD2 · 1 optical · 1 heat · 2 multi-sensor · 1 CO
Produces an A4 PDF with the property details, device schedule, room-by-room siting notes, the standards list and a sign-off block.
Disclaimer — no liability
This tool is an indicative planning aid, not a site survey, a fire risk assessment or a certified design. Every design must be confirmed by a competent person against the actual layout, escape strategy, occupancy, the local housing authority’s HMO standards, the manufacturer’s instructions and the current editions of BS 5839-6:2019+A1:2020, BS 5839-1:2017, BS EN 50291 and BS 7671:2018+A4:2026.
All Cabling© Limited accepts no liability whatsoever for any loss, damage, injury, cost or non-compliance arising directly or indirectly from use of, or reliance on, this tool or its output. By using it you accept these terms in full.