Only ever had one false alarm from those in 20 years. When I came home, there was a perfect imprint of a pigeon with wings outstretched in white dust on the outside of the glass, although it hadn't broken the glass.
Alarm question - PIRs, window contacts or optical boundary?
Sep 27, 2017
42 Replies
That's called double-knock. Some systems are configured so the second event must come from a different sensor, but that's only viable if you have enough sensors separately connected to the panel that any intruder is pretty much guaranteed to trip more than one. It can also delay the alarm so that instead of sounding before the intruder gains entry, the alarm is only raised after gaining entry, and that's not necessarily good, although it significantly reduces false alarms.
Double-knock is obligatory if you want police response.
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