Audibility — the requirement most premises fail
An alarm that cannot be heard is not an alarm. BS 5839-1 requires a minimum of 65 dB(A) in all accessible areas, or 5 dB above any background noise that persists for more than 30 seconds, whichever is greater. Where people sleep, the requirement rises to 75 dB(A) at the bedhead. In practice, premises fail this for predictable reasons: a noisy plant room or commercial kitchen where background noise exceeds the sounder output, a partitioned office where new walls have blocked sound paths, a toilet block or store room with the door closed, or simply a building extended without additional sounders. We take sound level readings in occupied areas rather than assuming a sounder that beeps is a sounder that works.