Abstract: 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.