Abstract: An intrusion detection system which reliably detects intrusions while minimizing false alarms by time-analyzing significant signals indicative of intrusions. The time length of each significant signal is measured, the time lengths of successive significant signals are accumulated, and an intrusion signal is generated if the accumulated time length reaches a first preselected time length. The time length between successive significant signals is also measured, and the accumulated time length is reset to zero if the time length between successive significant signals reaches a second preselected time length.