Heat alarm, fixed 135°F

A garage, an attic, a boiler room or a dusty workshop will set a smoke alarm off often enough that somebody eventually takes the battery out — and an alarm with no battery is worse than no alarm, because everyone believes the room is covered. A heat alarm ignores smoke and dust entirely and triggers on temperature: fixed at 135°F, plus a rate-of-rise element that fires earlier on a fast fire.

Sealed ten-year battery, and it interlinks with the wireless alarms on plate 14, so a garage fire wakes the house. It is not a substitute for a smoke alarm in a living space; it is the correct device for the rooms where one will not survive.

Fitting and care. Ceiling mount in the centre of the space where possible; heat alarms rely on hot gas collecting at the ceiling and a unit in a corner or on a wall responds late. Do not fit one where a smoke alarm belongs — it will not detect a smouldering fire and it is not a substitute in a living space. Test monthly. In an unheated garage or attic, check it after the first hard frost and the first hot spell, which is when the electronics in cheap units fail.