What is an automatic fire detector?
An automatic fire detector senses a fire and signals the control panel without anyone acting. The common types sense smoke, heat or flame, and each suits different rooms and different risks.
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<img src="https://fireoptix.co.uk/glossary/automatic-detector/diagram.svg" alt="automatic fire detector — diagram from FireOptix" width="880" height="620" loading="lazy">
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<a href="https://fireoptix.co.uk/glossary/automatic-detector">What is an automatic fire detector?</a> — diagram by
<a href="https://fireoptix.co.uk">FireOptix</a>
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</figure>Type selection is the whole of the design problem. A smoke detector in a kitchen produces false alarms until somebody disables it; a heat detector in a bedroom responds too late to be useful. Putting the right type in the right room is what makes a system trusted.
Detectors have a service life and a sensitivity that drifts. They are cleaned and replaced on a cycle, and a detector that has been in place indefinitely is either less sensitive than intended or more prone to false alarms.
Coverage is decided by the system's category, which follows from what the system is protecting — life, property, or both — rather than from how many detectors the budget allows.
In practice
A detector covered with a bag during dusty work and never uncovered.
Covering it was correct. The bag is still there a fortnight later, and the panel shows no fault because a covered detector looks healthy.
Isolations and coverings are windows during which a space is unprotected, and the record of putting one in is useless without a record of taking it out.
Nothing on a panel tells you a detector is wearing a bag.
What goes wrong in practice
- Detectors covered during building work to stop false alarms and never uncovered.
- The wrong type in a room, which reliably ends in the detector being disabled.
- Obstructed by new partitions, ductwork or storage stacked too close to the ceiling.