Systems and methods are provided for detecting changes in a monitored environment. One aspect of the invention relates to a system that comprises a plurality of radio frequency (RF) sensors distributed about the monitored environment, such that each RF sensor configured to respond to an interrogation signal with a unique identifier and a radio frequency (RF) interrogator that transmits interrogation sequences of interrogations signals over a plurality of different frequency bands at one or more power levels. The system also includes a response pattern analyzer that determines response patterns for each of the plurality of RF sensors to the interrogation sequences and transmits a change detection indicator if at least one of the determined response patterns vary outside a predetermined background baseline.