Types of Smoke Alarm for Landlords in London — Grade D vs Grade A Explained
London landlords must understand the difference between Grade D battery-operated alarms (suitable for most single lets) and Grade A panel-controlled systems (mandatory for HMOs with three or more storeys). This guide explains BS 5839-6 grades and categories, costs, and what your property legally requires.
The Two Alarm Grades: D and A
British Standard BS 5839-6:2019 (Fire Detection and Fire Alarm Systems for Buildings — Code of Practice for the Design, Installation, Commissioning and Maintenance of Fire Detection and Fire Alarm Systems in Domestic Premises) categorises alarm systems primarily by how they are powered and controlled.
Grade D: Mains-powered smoke alarms with a standby battery backup, self-contained (no control panel). This is the standard for most London rental properties. Each alarm contains its own detection, sounder, and power supply. Alarms are interlinked wirelessly or via cable so that when one activates, all sound. Cost per alarm: £30-80. Typical single-let installation: £150-350 for 3-4 alarms professionally fitted and tested.
Grade A: A full fire detection and alarm system controlled by a central control panel, with automatic detectors, manual call points, and separate sounders. Mandatory for HMOs with three or more storeys. The panel monitors every device and can identify exactly which detector has activated. Cost: £1,500-5,000+ for residential HMO installation depending on size and category.
BS 5839-6 Categories — What L1 to L5 Mean
The system category describes where detectors are installed:
- Category LD1: Detectors throughout all areas of the dwelling including roof spaces, sub-floor voids, and wall cavities where fire could start — maximum protection
- Category LD2: Detectors in all escape routes (hallways, landings, stairwells) plus rooms that present the highest risk such as kitchens and principal habitable rooms — the most common standard for HMO licensing
- Category LD3: Detectors on escape routes only (hallways, landings, stairwells) — minimum standard for single-occupancy lets under the 2022 Regulations
- Category PD: Property protection categories (PD1 and PD2) — detectors specified to protect property rather than life. Not typically specified for rental properties
What the Law Requires for London Rental Properties
The Smoke and Carbon Monoxide Alarm (Amendment) Regulations 2022 (applicable since October 2022) require:
- At least one smoke alarm on every storey used as living accommodation — minimum LD3 coverage
- CO alarm in every room with a fixed combustion appliance
- Alarms must be in working order at the start of each new tenancy
For HMOs, the Housing Health and Safety Rating System (HHSRS) and HMO licensing conditions applied by London boroughs specify higher standards. Most boroughs require at minimum a Grade D, Category LD2 system for HMOs. Properties with three or more storeys above ground floor require a Grade A system in most borough licensing schemes.
Interlinked Wireless Systems
Modern Grade D alarms can be interlinked wirelessly using radio frequency protocols (Ei RF or ZigBee), meaning installation does not require cabling between alarm positions. This is practical for tenanted properties and for period buildings where cabling would require extensive making good. Brands including Aico 3000 series and Ei650 series provide reliable wireless interlinking certified to BS 5839-6.
All new Grade D installations for rental properties should use interlinked alarms. A standalone smoke alarm that does not trigger alarms elsewhere in the property provides inadequate warning — particularly in multi-storey properties or those where bedrooms are remote from kitchens.
Carbon Monoxide Alarms
CO alarms must comply with BS EN 50291-1:2018 (electrochemical sensor type). The 2022 Regulations do not specify Grade D for CO alarms — battery-operated alarms are compliant. However, for HMOs and larger properties, mains-powered CO alarms interlinked with the smoke alarm system provide better reliability and are increasingly specified in HMO licensing conditions.
Frequently asked questions
Does my London rental property need interlinked smoke alarms?
The 2022 Regulations require smoke alarms on every storey but do not explicitly mandate interlinking for single-let properties. However, BS 5839-6 guidance and best practice strongly recommends interlinking — an alarm that only sounds in the affected room provides inadequate warning in a multi-storey property. Most landlords and installers now specify interlinked Grade D alarms as standard.
At what point does an HMO need a Grade A fire alarm system?
The specific threshold varies by London borough, but most borough licensing schemes require a Grade A system for HMOs with three or more storeys. Some boroughs require Grade A for all HMOs with five or more occupants regardless of storeys. Check the specific conditions attached to your HMO licence or the borough's published licensing requirements.
How often do smoke alarm batteries need to be replaced in a rental property?
For Grade D mains-powered alarms with a sealed 10-year lithium battery backup, the entire alarm unit is replaced every 10 years. For alarms with replaceable batteries, batteries should be replaced annually. The landlord is responsible for ensuring alarms are in working order at the start of each tenancy; battery checking during tenancy is the tenant's responsibility under the 2022 Regulations.