Smoke and Carbon Monoxide Alarms in UK Homes: 2022 Regulations, Placement Rules, and Alarm Types

Smoke and Carbon Monoxide Alarms in UK Homes: 2022 Regulations, Placement Rules, and Alarm Types

The Smoke and Carbon Monoxide Alarm (Amendment) Regulations 2022 (England) significantly extended the requirements for alarm installation in rented properties and new builds. For electricians, builders, and landlords, understanding what is now legally required — and what constitutes best practice beyond the minimum — is essential. This guide covers the current legal requirements, alarm placement rules, and the technical differences between alarm types.

Current Legal Requirements (England, from 1 October 2022)

The Smoke and Carbon Monoxide Alarm (Amendment) Regulations 2022 amended the 2015 Regulations and extended their scope:

For Private Rented Properties (all tenures)

• Smoke alarms: At least one smoke alarm on every storey of the property where there is a room used as living accommodation
• Carbon monoxide alarms: At least one CO alarm in any room used as living accommodation which contains a fixed combustion appliance (gas boiler, solid fuel appliance, wood-burning stove, gas fire) — this is the 2022 extension that added gas appliances to the previous solid-fuel-only requirement
• Alarms must be tested and in working order at the start of each tenancy
• Landlords must repair or replace alarms within a reasonable time of being notified of a defect

For New-Build and Change-of-Use Dwellings (Building Regulations Part B)

• Smoke alarms in every principal room, every circulation space on each storey (hall, landing), and in every bedroom
• All alarms must be mains-powered with battery backup (LD1 or LD2 grade systems for domestic dwellings per BS 5839-6)
• All smoke alarms in the same dwelling should be interlinked — when one triggers, all sound
• CO alarms required in rooms with combustion appliances

Scotland, Wales, Northern Ireland

Scotland has additional requirements including heat alarms in kitchens and mandatory interlinking. Wales aligns broadly with England's 2022 regulations. Always check the relevant devolved nation regulations for properties outside England.

Smoke Alarm Placement Rules

Correct placement is as important as having alarms installed:

• Ceiling mounted: Smoke alarms should be ceiling-mounted in the centre of the room or ceiling — at least 300mm from any wall or light fitting, and at least 500mm from a ceiling rose or any obstructions. The centre of the ceiling maximises detection as smoke rises and spreads outward.
• Circulation spaces (hallway, landing): One alarm per storey in the circulation space — positioned to be between the bedroom doors and the escape route. A hallway alarm between bedrooms and the stairwell is the classic location.
• Bedrooms: Best practice and Part B new-build requirement — an alarm in every bedroom. If a bedroom has an electric heater or TV that could smoulder overnight, in-bedroom alarms significantly reduce risk.
• Avoid kitchens: Standard ionisation and optical smoke alarms should not be placed in or immediately adjacent to kitchens — cooking fumes cause nuisance alarms. Use a heat alarm in the kitchen instead (responds to temperature rise, not smoke particles).
• Avoid bathrooms: Steam from showers causes false alarms. No alarms in bathrooms — the circulation space alarm covering the landing is sufficient.
• Near garage doors: Avoid positioning alarms within 3m of any integral garage door — diesel/petrol fumes cause nuisance activation.
• High-ceiling properties: In rooms with vaulted or cathedral ceilings above 3.5m, position the alarm at 500mm below the apex of the ceiling — smoke banks at the highest point.

Smoke Alarm Types: Ionisation vs Optical

Ionisation Alarms

Ionisation alarms contain a small radioactive source (Americium-241) that ionises air in a detection chamber. Smoke particles disrupt the ion current and trigger the alarm. Ionisation alarms are faster at detecting small, fast-flaming fires (paper, chip pan fires) but are more susceptible to nuisance alarms from steam and cooking.

Best placed in: Living rooms, bedrooms, and hallways away from kitchens.

Optical (Photoelectric) Alarms

Optical alarms use an LED and photodiode. In the absence of smoke, the LED beam misses the photodiode. Smoke particles scatter the light, redirecting some onto the photodiode and triggering the alarm. Optical alarms are better at detecting slow-burning, smouldering fires (furniture, wiring fires, which produce larger smoke particles) and are less prone to nuisance alarms from cooking.

Best placed in: Living rooms, bedrooms, landings — particularly in properties where a nuisance alarm from ionisation would be problematic.

Multi-Sensor Alarms

Combine optical and heat sensors (or optical and ionisation). More accurate detection across fire types with fewer nuisance alarms. Recommended where a single alarm type must serve a wider area. Particularly suitable for the main hallway/landing alarm in a domestic property.

Heat Alarms

Heat alarms respond to temperature rise rather than smoke particles. Available as fixed temperature (triggers at a set temperature, typically 58°C or 90°C) or rate-of-rise (triggers when temperature rises rapidly, regardless of absolute value). Heat alarms are mandatory in kitchens under Scottish regulations and are best practice in kitchens throughout the UK — they do not false-alarm from cooking. They are not a substitute for smoke alarms elsewhere.

Carbon Monoxide Alarms

CO alarms detect carbon monoxide gas — the colourless, odourless product of incomplete combustion from gas boilers, gas fires, wood-burning stoves, open fires, and solid fuel appliances. CO kills silently — victims are often unaware of exposure until incapacitated.

Placement:

• In the same room as the combustion appliance — typically the boiler cupboard (if accessible), living room (for gas fire or stove), or utility room
• At breathing height (1m–1.5m from the floor) — CO is slightly lighter than air but mixes throughout a room under normal conditions
• Not directly above or adjacent to a combustion appliance — the alarm will detect normal start-up emissions and false alarm. Position at least 1–3m from the appliance.
• Not in enclosed spaces (inside a boiler cupboard with the door typically closed) where the alarm cannot alert occupants. The alarm should be audible from sleeping areas when triggered.

Types:

• Electrochemical sensor: The most common and accurate CO detection technology. An electrochemical cell produces a measurable current proportional to CO concentration. Battery life is typically 5–7 years and the sensor itself has a defined life (5–10 years depending on manufacturer) — CO alarms should be replaced when the sensor expires even if the unit is functional.
• Combined smoke and CO alarms: A convenient single unit combining both functions. Useful where only one position is practical, or where the CO source is in a living space that also needs smoke detection. Not suitable as a kitchen replacement for a heat alarm.

Sensor life: CO alarm sensors degrade over time. An alarm that is 7+ years old may not respond adequately to CO even if the low-battery warning functions. Always advise customers to check the manufacture date and replace accordingly.

Mains vs Battery Alarms

• Mains-powered with battery backup (230V with 9V or lithium backup): Required for new-build dwellings under Building Regulations Part B. More reliable — a flat battery does not take the alarm offline. Requires an electrician for installation (Part P notifiable work if a new circuit or spur is involved). All alarms in the dwelling should be interlinked via a wiring loom or wirelessly.
• Battery-only (9V or 10-year lithium sealed): The minimum standard for rented properties under the 2022 Regulations — the landlord is not required to install mains-powered alarms in existing properties. 10-year lithium sealed battery alarms are the best battery option — the battery is sealed and cannot be removed, eliminating the risk of a removed battery. Alarm and battery can be replaced together after 10 years.
• Wireless interlinked battery alarms: Allow all alarms in a property to be interlinked without electrical wiring — when one triggers, all sound. The preferred solution for retrofitting interlinked alarms to existing properties without running new cables.

Smoke and CO Alarms at APM Plumbing & Electrical

APM stocks a full range of smoke alarms, heat alarms, and carbon monoxide alarms for domestic and light commercial installation. Our range includes battery-only 10-year lithium sealed alarms (ideal for landlord compliance), mains-powered alarms with battery backup for Part B new-build installations, and wireless interlinked systems for retrofit properties. We stock both optical and ionisation smoke alarms, multi-sensor alarms for hallways, combined smoke/CO detectors, and standalone electrochemical CO alarms from Aico, FireAngel, and compatible trade brands.

Browse our smoke and CO alarms or visit the Acton trade counter. Trade orders placed before 2pm ship same day across London and the South East.

Products Available from APM Plumbing & Electrical

Key smoke and CO alarms available for trade collection or delivery:

Get It from APM Electricals

APM Electricals, 24 Western Avenue, Acton, London W3 7TZ. Call 020 8702 8080 or visit www.apmi.uk for same-day trade counter collection and next-day delivery across London and the UK.