Abstract: A monitoring system determines the presence of the person or persons to be monitored within a well-defined area or areas using one or more portable remote devices which are in two-way communication contact with a base unit. The base unit is connected to a telephone line to enable communication with a monitoring service. The base unit and remote unit incorporate spread spectrum communication technology which permits a high transmit power level. The effectiveness of the monitoring system does not depend on radio signal strength, but instead, operates using a radio ranging method that measures the time it takes for a security-coded signal to be transmitted to and returned from the remote device. The remote device also includes a mechanism for sounding an audible out-of-range warning alarm in the event that the person being monitored exceeds the house arrest boundaries.