On 02/08/2018 16:20, Brian Gaff wrote:
I've got a fire alarm older than that and it still goes off when you do
toast in the kitchen downstairs. it alls bleeps when its battery is going
down, usually in the middle of the night.. Its only those with radioactive
sources that wear out I think.

Most are the ionisation type...

How do the others work?

Optical detection or heat detection.

(the optical ones also "age" due to dust etc, and the heat detectors are
not effective as general purpose early warning alarms)

--
Cheers,

John.

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