Abstract: A pulsed conductivity sensor intrusion detection device which uses the conduction of short electrical pulses on or near the surface and the immediately adjoining air above the surface. An intruder causes the propagated signal to change which is sensed by the Pulsed Conductivity Sensor (PCS) and produces an alarm. A path is protected by placing a transmitter and a receiver on either side with the protected region between them. An area is protected by placing transmitter and receivers around the periphery of the area. Pulses are sent from the transmitter to the receiver through the surface and the air immediately above it. The receiver sends the signal to an analyzer where the frequency/amplitude spectrum is determined using Fourier Transform techniques. Pulses are sent ten or more times per second and each is analyzed. By comparing sequential pulses, any change will be detected. Signatures for different subjects have been determined and are used to detect when a human intrusion occurs.