Every type of smoke alarm, explained
The differences that matter are not cosmetic. Power source decides whether the alarm survives a power cut; the interconnection decides whether everyone in the building hears it; the sensing technology decides whether it cries wolf.
By power source
Battery-only (standalone)
A 9 V alkaline, a 9 V lithium or a sealed 10-year lithium cell. No wiring, installable in minutes, suited to older buildings and rented flats. The failure mode is human: the battery is removed to silence a nuisance alarm and never replaced.
Typical life: 1 year (alkaline), 5–10 years (lithium), 10 years (sealed)Mains-powered with battery backup
Runs from the building supply with a rechargeable or replaceable backup cell. No routine battery changes, and the units can be wired together so that one alarm sounds them all. Requires a permanent, fused, regularly used lighting circuit — never a switched socket.
Typical backup: 7 days standby or 4 minutes in alarmIn Europe and North America the tamper-proof sealed unit is now the usual specification for rented housing, precisely because it cannot be raided for a battery. Where legislation requires a 10-year sealed unit, a removable-battery alarm does not comply even if its battery happens to be lithium.
By interconnection
| Arrangement | How it works | Strengths | Watch out for |
|---|---|---|---|
| Standalone | One device, one sounder | Cheapest; no wiring; ideal for a single room | Nobody hears an alarm that fires in a closed room at the far end of the house |
| Hardwired interlink | A communication conductor between mains units, usually three-core plus earth | Deterministic, no radio, no battery dependency for the link, no pairing | Requires cable and a competent electrician; hard to retrofit into a finished home |
| Wireless interlink | Sub-GHz or 2.4 GHz radio mesh between units | Retrofits into any building; mixes mains and battery units; pairs in minutes | Radio range through reinforced concrete or metal; pairing and house-coding must be done properly |
| System with panel | Detectors on a loop reporting to a control panel | Zonal identification, monitored circuits, integration with sounders, beacons and call points | Design and commissioning by a qualified contractor; not a homeowner product |
By capability
Smart / connected
Wi-Fi or hub-based devices that push notifications to a phone, log events, allow remote inspection of status and can be silenced from an app — but keep a full local 85 dB sounder and must work with the internet down.
Smart & connectedHeat detectors
Fixed temperature around 57–58 °C, rate-of-rise, or both. The correct device for kitchens, garages, boiler rooms and dusty workshops — and deliberately slow on smouldering fires.
Special environmentsCombined CO + smoke
Two hazards in one housing. Convenient, but the CO channel follows its own standard and its own maintenance logic — check that the certificate covers both.
Certified to EN 14604 and EN 50291 (or UL 217 and UL 2034)Grades and categories — the language of fire codes
British and many European specifications describe what you install with a letter grade and where you install it with a category. Once you can read the two together, a specification such as “Grade D2, LD2” stops being jargon and becomes an instruction.
| Grade | What it means |
|---|---|
| Grade A | Separate detectors on a fire panel, with sounders — used in large or complex residential buildings |
| Grade B | Separate detectors and sounders on a control unit, with central power |
| Grade C | Separate detectors and sounders on a control unit, using local mains power |
| Grade D | One or more mains-powered smoke alarms with a standby supply — the common domestic specification |
| Grade E | Mains-powered smoke alarms without a standby supply (no protection in a power cut) |
| Grade F | Battery-only smoke alarms — the minimum where nothing else is practicable |
| Category | Coverage |
|---|---|
| LD1 | Highest: alarms in all circulation areas plus every room where a fire could start, apart from rooms with a low fire risk |
| LD2 | Aimed at escape routes: circulation areas plus the rooms used as sleeping accommodation and the principal living space |
| LD3 | Escape routes only: circulation areas between the sleeping area and the final exit |
Grades and categories are design language, not law in themselves — the law cites them. National and regional requirements differ widely and change regularly, so check the standards and regulations page and confirm locally before specifying.
Practical selection in four questions
- Is this a dwelling or a managed building?A dwelling almost always takes Grade D or F self-contained alarms. Any building with a fire strategy, sleeping strangers or an evacuation plan usually needs a panel-based system.
- What is the room?Smoke sensing for circulation and sleeping spaces; heat sensing for kitchens, garages and dusty rooms; CO sensing where combustion appliances or vehicle exhaust can leak in.
- Do all the devices need to sound together?In almost every occupied building, yes. Wireless interlinking lets you achieve that without opening ceilings.
- Who will maintain it?A landlord, a maintenance contractor and a family in a private house need different accessibility. Choose units whose test, silence and replacement you can actually perform.
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