A robust, easily deployable, covert, passive intrusion detection system uses one or more E-field sensors to detect the presence of a moving individual and to provide an indication of the presence of the individual adjacent the sensor based on E-field distortion produced by the individual. Single-ended and differential E-field sensors with noise canceling and a guarding circuit provide sufficient sensitivity, with filtering from 0.5 Hz to 8.0 Hz selecting only human intruders. Either visible or invisible flashing light sources at the sensor indicate the presence of a moving individual at the sensor, thus to provide intruder location without the necessity of providing a geolocation system.