What is a sounder?
A sounder is the device that produces the audible alarm signal. Sounders must be loud enough to be heard everywhere people may be, including over background noise and through closed doors.
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<img src="https://fireoptix.co.uk/glossary/sounder/diagram.svg" alt="sounder — diagram from FireOptix" width="880" height="620" loading="lazy">
<figcaption>
<a href="https://fireoptix.co.uk/glossary/sounder">What is a sounder?</a> — diagram by
<a href="https://fireoptix.co.uk">FireOptix</a>
</figcaption>
</figure>Audibility is measured in the places people actually are, not in corridors. A workshop with machinery running, a hotel bedroom with the door shut and a plant room are the conditions the coverage has to satisfy.
Where audibility alone cannot work — for sleeping occupants, for people with hearing loss, or in very noisy areas — visual beacons or vibrating devices supplement the sounders rather than replacing them.
A distinct alarm signal matters as much as volume. Occupants who cannot distinguish the fire alarm from another building alarm will wait to be told, which is the delay the system exists to remove.
In practice
A plant room where the alarm cannot be heard over the machinery.
The weekly test is carried out from reception and the person testing does not walk the building.
Audibility is what the test is actually checking, and the areas where it fails are the noisy ones, the isolated ones and the ones behind closed doors.
A tick for 'sounders operated' records the panel rather than the building.
What goes wrong in practice
- Coverage assessed in corridors rather than in the rooms and conditions people are in.
- Areas added in a refurbishment with no sounder extension.
- Provision for occupants with hearing loss left out of the design entirely.