In article ,
Andy Burns wrote:
Dave Plowman (News) wrote:

Piezo sounders tend to be tuned to a particular highish frequency for
best efficiency. Perhaps ideal for an alarm

The beat frequency you get when multiple sounders are e.g. on each floor
of a staircase, seem to be set to the resonant frequency of a skull, for
maximum annoyance while you're trooping down to the fire-exit

A former colleague mouted a 12" loudspeaker on the stairwqll ceiling.
OPeating the bell push triggered a tape loop of the Westminster Chimes. You
heard them even when in the garden!

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from KT24 in Surrey, England