Grade D under BS 5839-6:2019 means an alarm powered from the mains supply with an integral standby battery capable of running the alarm for at least 72 hours. The mains feed is taken from the lighting circuit (not a socket — so the alarm is always live when the main switch is on) and the battery is sealed for the full ten-year life of the head. There is no battery to change and no annual chirp at 3am.
Since the Smoke and Carbon Monoxide Alarm (England) Regulations 2015 were amended in October 2022, Grade D (or better) is the mandatory standard in every English rental, regardless of when the property was built or converted. Grade F — battery only — remains legal for owner-occupied homes but is no longer accepted by London licensing boroughs for HMOs or rental compliance audits.
Electrician London installs Grade D systems at £180 per point covering the alarm, the wiring, the interconnect and the BS 5839-6 commissioning certificate. Aico, FireAngel and Kidde heads are all available — the survey identifies the right schedule and the right head for each room.
Why Electrician London
Mains-powered with battery backup
Lighting-circuit feed plus a sealed 72-hour lithium standby. Survives the power cuts that take out battery-only alarms first.
BS 5839-6:2019 compliant
Designed, installed and commissioned to the current standard. Certificate handed over on the day for licensing renewals.
Mandatory in English rentals
Required under the 2015 Regs as amended October 2022. Every London licensing borough audits to this standard.
Ten-year sealed battery
No annual battery change, no 3am chirp. End-of-life means head replacement, which we do like-for-like at £180 per point.
Grade D smoke alarm pricing
Per-point pricing covers alarm, wiring, interconnect and certificate.
Grade D smoke alarm install
Mains + battery, BS 5839-6
£180 / point
Grade D heat alarm (kitchen)
Mandatory in kitchens under LD2
£170 / point
Grade D interlinked system (3-4 alarms)
Typical 1-2 bed HMO or family home
£550
Grade D HMO upgrade (5-7 alarms)
Full LD2 schedule, multi-storey HMO
£750-£1,400
Annual BS 5839-6 inspection
Engineer test, logbook entry
£85
What's included in a Grade D install
- Mains supply taken from the lighting circuit
- 72-hour sealed-battery backup
- BS 5839-6:2019 compliant alarm head
- Wired or radio-linked interconnect
- LD2 schedule designed to the property
- Commissioning test under load
- BS 5839-6 certificate and logbook
- Minor Works Electrical Installation Certificate
Frequently asked questions
What does Grade D actually mean?
Grade D is BS 5839-6 shorthand for "mains-powered with an integral standby battery capable of at least 72 hours of standby plus four minutes of alarm". In practice it is what the regulations and the London licensing boroughs expect on every rental property — mains feed plus sealed lithium backup.
When did Grade D become mandatory in rentals?
The Smoke and Carbon Monoxide Alarm (England) Regulations 2015 originally allowed battery-only alarms (Grade F). The October 2022 amendment extended the duty to all rented homes (previously only private rented) and tightened the working-alarm requirement. Combined with BS 5839-6:2019, Grade D is now the de-facto rental standard.
What is the 72-hour battery rule?
The standby battery must be able to maintain the alarm in quiescent (listening) mode for at least 72 hours after mains failure, then sound for at least four minutes if smoke is detected. Modern sealed-lithium alarms exceed this by a factor of three.
Where is Grade D allowed and where is it required?
Required in every English rental and HMO. Required in new-build domestic property under Building Regulations Part B. Allowed everywhere as a voluntary upgrade. The only setting where Grade F (battery only) remains practical is owner-occupied homes — and even then, mains-powered Grade D is the safer choice.
Can I get Grade D radio-linked?
Yes. Aico Ei3000-series, FireAngel Pro and Kidde Multipro all offer radio-link modules that snap into a Grade D base. The base still wires to mains, the radio module just handles the interlink signal. Identical compliance to hard-wired.
How long do Grade D alarms last?
Ten years from the date stamped on the head. After ten years the head chirps end-of-life and must be replaced. We replace like-for-like at £180 per point on existing wiring.
Why feed from the lighting circuit?
BS 5839-6 requires the mains feed to come from a circuit that is on whenever the main switch is closed. The lighting circuit is the standard choice because it is always live when the consumer unit is on and any tripping is immediately obvious to occupants. Sockets are not allowed because they can be unplugged.
Can I upgrade an existing Grade F installation to Grade D?
Yes. We remove the battery-only heads, run a feed from the lighting circuit to each location, fit Grade D bases and commission the new system. Typical 3-bed conversion costs £550-£750 depending on cable routing. The replacement is a Minor Works job under BS 7671.
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