An improved system and method for monitoring objects, people, animals, or places uses a passive Modulating Reflector (MR) tag where an antenna is alternately short and open circuited according to a time-varying pattern by a modulating network thereby causing the reflective characteristics of the antenna to vary in accordance with the time-varying pattern. When an interrogator transmits an RF waveform that impinges on the antenna, the return signal reflecting off the antenna is modulated in accordance with the time-varying pattern allowing a remote receiver to demodulate information from the modulated return signal. The MR tag can be used with a wide variety of tag-interrogator configurations employing monostatic and/or bistatic radar techniques to allow monitoring, locating, and/or tracking of objects, people, animals, or place with which MR tags are associated.