On 15/01/2004 Mortimer opined:-
What sort of alarm system should I go for, PIRs seem simple to
source and install but are there any that ignore cats and only react
to humans?

No, but you could probably site them so that they wouldn't 'see' a cat
on the ground. Even a bit of black insulation tape is enough, when
placed across the lens to restrict the field of view of a PIR.

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Regards,
Harry (M1BYT) (Lap)
http://www.ukradioamateur.org