Smoke Alarms and Carbon Monoxide Detectors — Regulations, Positioning, and Replacement for UK Homeowners and Electricians

Smoke alarms and carbon monoxide (CO) detectors are legal requirements in UK residential properties — and choosing the right type, positioning them correctly, and replacing them on schedule is essential for both compliance and life safety. This guide covers what UK regulations require, the difference between optical, ionisation, and thermoptek detection, and which products to stock for domestic and light commercial installations.

UK Legal Requirements for Smoke and CO Alarms

The Smoke and Carbon Monoxide Alarm (Amendment) Regulations 2022 (England) require landlords to install smoke alarms on every storey used as living accommodation, and CO alarms in any room with a fixed combustion appliance (gas boiler, log burner, open fire). These rules apply to all private rented properties since 1 October 2022. Scotland, Wales, and Northern Ireland have separate but similar legislation.

For new builds and full renovations, Approved Document B (fire safety) and Approved Document J (combustion appliances) set interlinked mains-powered alarm requirements. BS 5839-6 provides the detailed specification for domestic fire alarm systems — installers working on private rental or new-build properties need to be familiar with Grade D (mains with battery backup) and Grade F (battery-only) systems.

Alarm Detection Technologies

Not all smoke alarms detect the same type of fire. Choosing the right sensor technology for the room matters:

• Optical (photoelectric): Best for slow-smouldering fires — common in living rooms and bedrooms. Slower to trigger in fast-flaming fires but fewer false alarms from cooking fumes. The Aico Ei146e uses optical detection.
• Ionisation: Faster to respond to fast-flaming fires with small particles. More prone to nuisance alarms from cooking — not recommended near kitchens.
• Thermoptek (dual sensor): FireAngel's proprietary technology combining optical and heat sensors. Reduces false alarms significantly versus ionisation-only alarms while maintaining fast response. The ST-632 uses Thermoptek detection and is one of the most specified battery alarms for UK domestic use.
• Heat: Responds to temperature rise rather than smoke — ideal for kitchens and garages where other detectors would nuisance alarm. Fixed temperature or rate-of-rise types available.

Carbon Monoxide (CO) Detectors

CO is colourless and odourless — a detector is the only way to know if levels are rising. CO alarms are required in any room with a gas, oil, or solid fuel appliance. The EN 50291 standard governs CO alarm performance in the UK.

Key installation rules:

• Position CO alarms at head height (breathing zone) or as directed by the manufacturer — typically 1–3 metres from the appliance
• Do not position directly above a gas hob or in a sealed cupboard
• Do not fit in boiler cupboards where CO may accumulate and trigger false alarms
• Replace when the end-of-life warning sounds — typically 7–10 years depending on model

Battery vs Mains-Powered Alarms

For rental properties and refurbishments, battery alarms are common where retrofitting mains wiring is impractical. 10-year sealed battery alarms are the current best practice — they eliminate the risk of tenants removing batteries when the low-battery chirp activates, and they last the full expected life of the alarm before replacement.

For new build and full renovation projects, mains-powered with battery backup (Grade D to BS 5839-6) is the standard. Interlinked alarms — where one detector triggering sounds all alarms in the property — are increasingly common even in battery systems via radio interlinking (no wiring required between units).

Positioning Rules (BS 5839-6)

Standard positioning for smoke alarms:

• On the ceiling, at least 300mm from walls and light fittings
• At least one alarm per storey of a dwelling
• In all rooms used as living accommodation (rental requirement from 2022)
• Avoid positioning within 3m of a cooking appliance
• Avoid bathrooms, garages, and areas subject to condensation

In practice, most installers fit a smoke alarm in the hallway and landing, and a heat alarm in the kitchen. Properties with solid fuel appliances also need a CO alarm in any room with a stove or open fire.

Interlinked Alarms

Interlinked alarms sound all units when any one triggers — essential in larger properties and required under BS 5839-6 Category LD2 or LD1 systems. Radio interlink eliminates the need for hardwiring between units, making it practical for retrofit installations. The FireAngel ST-632 supports radio interlinking with compatible FireAngel devices.

Alarm Replacement Schedules

Smoke alarms and CO detectors have a defined service life:

• Smoke alarms: typically 10 years from manufacture date (check label on base)
• CO alarms: 7–10 years depending on model (check end-of-life indicator)
• Sealed 10-year battery models: replace entire unit at end of battery life

Landlords and housing managers should log installation dates and set replacement reminders. Many electricians now include alarm checks in annual inspection visits.

Products Available from APM

Choosing the Right Alarm for the Job

A simple guide for common situations:

• Rental property retrofit: FireAngel ST-632 (hallway/landing) + Arctic Hayes COA10 (boiler room/kitchen) — 10-year sealed battery, minimal maintenance
• New build or rewire: Aico Ei146e (mains optical, interlinkable) across all habitable rooms; add CO alarm in any combustion appliance room
• Kitchen/garage: Heat alarm — avoid smoke detectors in these locations
• Larger property with solid fuel stoves: Interlinked system with CO alarms in every room containing a stove or open fire

Summary

UK regulations now require smoke alarms on every habitable storey and CO alarms in any room with a combustion appliance. 10-year sealed battery models like the FireAngel ST-632 and Arctic Hayes COA10 are the most practical choice for rental retrofits — no battery maintenance risk. For new build and full renovation, mains-powered interlinked alarms to BS 5839-6 Grade D are the correct specification. APM stocks a range of smoke, CO, heat, and combination alarms from FireAngel, Aico, Arctic Hayes, and Kidde.

Browse our full range of smoke and CO alarms or explore our safety products at APM Electricals.

APM Electricals — 24 Western Avenue, Acton, London W3 7TZ
Call us: 020 8702 8080 | www.apmi.uk