It happens that Simon formulated :
The standalone mains-powered PIR sensor has a row of Knight-rider style red
LEDS, which should attract the attention of anyone peering in through a
window. OTOH, they'd look silly and possibly reduce security if the PIR was
installed outside.

What about mains failure? No mains, no working alarm system.

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Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk