An apparatus and method of monitoring mobile objects or persons utilizes the Global Positioning System satellites and cellular telephone communications. The apparatus may include first and second remote units adapted to be worn on the monitored person or object. These remote units would comprise the position and data sensors as well as the transmitter device to transmit the information back to a central tracking station. The remote units may be operative to monitor many data items such as system integrity, motion, temperature, audio, and the like in addition to position. This data would then be transmitted back to a central monitoring station operative to process and display the information. The system is also adapted to monitor persons in hazardous environments such as radioactivity or poisonous gases or even to monitor inanimate objects such as automobiles.