Smoke detectors vs heat detectors: where to use each

Choosing the right detector for each room is one of the simplest ways to make a fire alarm both safer and quieter. Put a smoke detector in the wrong place and it will cry wolf. Put a heat detector in the wrong place and it will react too late.

Optical smoke detectors

Optical detectors shine a light inside a chamber. When smoke enters, it scatters the light onto a sensor and the detector operates. They respond well to slow, smouldering fires, such as a cigarette on a sofa, which produce a lot of visible smoke.

• Use in: hallways, landings, stairs, bedrooms, living rooms and offices.
• Avoid in: kitchens, bathrooms, dusty areas and anywhere with steam or aerosols.

Older ionisation smoke detectors, which use a small radioactive source, are now rarely installed in the UK.

Heat detectors

Heat detectors respond to temperature rather than smoke. Fixed-temperature detectors operate at a set temperature. Rate-of-rise detectors operate when the temperature climbs quickly.

• Use in: kitchens, boiler rooms, garages and other areas where smoke detectors would cause false alarms.
• Avoid in: escape routes and sleeping areas, where early warning of smoke matters most.

BS 5839-6 recommends heat detectors in kitchens in homes, and Scotland's alarm rules require a heat alarm in every kitchen.

Multi-sensor detectors

Multi-sensor detectors combine optical smoke and heat sensing, and use the combination to decide whether there is a real fire. They are far less likely to react to steam or toast than a plain optical detector, while still responding quickly to a real fire.

• Use in: areas next to kitchens and bathrooms, hotel bedrooms, student rooms and anywhere with a history of false alarms.

Other types

• Beam detectors for large open spaces such as warehouses and atriums.
• Aspirating detectors that draw air through pipes to a sensitive detector, for server rooms, cold stores and heritage buildings.
• Carbon monoxide detectors that warn of CO poisoning from fuel-burning appliances. They are not fire detectors, and rented homes in England need them in rooms with fixed combustion appliances other than gas cookers.

Getting it right

Detector choice should come from the fire risk assessment and a survey of how each room is used. If a detector keeps going off, have it reviewed by a competent engineer rather than covering or removing it.