A method of determining the range from an interrogator to one or more transponders, the method comprising the steps of: A. in the interrogator transmitting an interrogation RF carrier for a selected interval; B. in each transponder receiving the carrier, rectifying it, and charging a power capacitor with the rectified carrier; when the power capacitor has power above a predetermined threshold powering a detector, C. in the interrogator, terminating the transmission of the interrogation RF carrier at the end of the selected interval and starting a timer; D. in each transponder: 1) sensing by the detector of a cessation of the incoming interrogation RF carrier and starting a delay interval, and 2) at the end of the delay interval transmitting an RF response; E. in the interrogator: 1) receiving the RF responses, and 2) calculating the distance to each transponder from the elapsed time between the cessation of transmission of the interrogation RF carrier and the receipt of the RF responses from the respective transponders as determined by the timer and from the delays associated with the responses from the respective transponders, wherein a first one of the transponders transmits its RF response after a basic delay interval, substantially greater than the round trip RF propagation time between the interrogator and the transponder, and the other transponders have delay intervals that are different multiples of the basic delay interval. A. in the interrogator transmitting an interrogation RF carrier for a selected interval; B. in each transponder receiving the carrier, rectifying it, and charging a power capacitor with the rectified carrier; when the power capacitor has power above a predetermined threshold powering a detector, receiving the carrier, rectifying it, and charging a power capacitor with the rectified carrier; when the power capacitor has power above a predetermined threshold powering a detector, C. in the interrogator, terminating the transmission of the interrogation RF carrier at the end of the selected interval and starting a timer; D. in each transponder: 1) sensing by the detector of a cessation of the incoming interrogation RF carrier and starting a delay interval, and 2) at the end of the delay interval transmitting an RF response; 1) sensing by the detector of a cessation of the incoming interrogation RF carrier and starting a delay interval, and 2) at the end of the delay interval transmitting an RF response; E. in the interrogator: 1) receiving the RF responses, and 2) calculating the distance to each transponder from the elapsed time between the cessation of transmission of the interrogation RF carrier and the receipt of the RF responses from the respective transponders as determined by the timer and from the delays associated with the responses from the respective transponders, wherein a first one of the transponders transmits its RF response after a basic delay interval, substantially greater than the round trip RF propagation time between the interrogator and the transponder, and the other transponders have delay intervals that are different multiples of the basic delay interval. 1) receiving the RF responses, and 2) calculating the distance to each transponder from the elapsed time between the cessation of transmission of the interrogation RF carrier and the receipt of the RF responses from the respective transponders as determined by the timer and from the delays associated with the responses from the respective transponders, wherein a first one of the transponders transmits its RF response after a basic delay interval, substantially greater than the round trip RF propagation time between the interrogator and the transponder, and the other transponders have delay intervals that are different multiples of the basic delay interval.