US Patent 6922145 Intrusion detection, tracking, and identification method and apparatus

Overlapping range rings from a pair of non-scanning radar or sonar transducers creates a grid structure within a surveillance area defined by their overlapping beam widths. Using PN coded transmission signals and doppler signal processing, intruder targets are detected, located, and tracked as they move throughout the grid structure. Intruders are identified by comparing their movement pattern to those of known intruders. Three dimensional surveillance areas can be monitored using three or more transducer sites.