1. A tag for transponding a radio frequency interrogator signal, comprising: a receiver for receiving the interrogator signal at a first frequency, said receiver being enabled for receiving only at pseudo-random intervals that are independent of generation times of said first frequency; a frequency mixer for generating from the received interrogator signal a radio frequency transmit signal at a second frequency; a microprocessor for generating a tag-specific data signal; a modulator for modulating the tag data signal onto the transmit signal to generate a first tag signal; and a transmitter for transmitting the first tag signal at selected times.