Smoke detectors use Americium with a half life of over 400 years so
after 10 years there is more than 98 per cent left. The replace "after
10 years" comes from risks of failure due to insects, grease, dust,
nicotine and other assorted gunk; and electrical failure - especially
where they are never tested (let alone tested with smoke).


On 20/04/2017 08:55, Brian Gaff wrote:
There seem to be two different sorts of smoke detector, most of the el
cheapo ones use a radioactive source the ionise the air and hence detect the
presence of smoke by the change in resistance so to speak. Others use a
laser beam system.
I think the problem with the radioactive ones is that as the isotope decays
the efficiency goes down, so after about 10 years its probably whatever the
sniffing equivalent is of deaf as a post.

Brian



--
Robin
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