A dual-sensing intrusion detection device for detecting an intruder
comprising a PIR sensor and a microwave sensor. The device comprises PIR
processing means and microwave processing means, means for summing the
processed PIR signal with the processed microwave signal to generate a
summed signal, and means for comparing the summed signal to a sum
threshold value to determine if an alarm condition exists. The sum
threshold value is selected for optimal discrimination between a human
intruder and an animal presence. An additional feature of the intrusion
detection device is the generation of a PIR difference signal. This
feature allows the device to compensate for the limited bandwidth of the
PIR sensor and to be more sensitive to a human intruder. The processing of
the sensor signals includes an integration technique that sums the
amplitude values of the signal and causes the sum to decay at a slow rate.
In addition, the slow decay rate causes the signal to be spread out in
time, thereby allowing the signals from both detectors to be above the
threshold at the same time.
