This is the same principle as long-range UHF RFID tags. There is a communications protocol (Gen2) that deals with collision detection and multiple access to al

This is the same principle as long-range UHF RFID tags. There is a communications protocol (Gen2) that deals with collision detection and multiple access to allow for hundreds (thousands?) of tags in the same space. Part of the protocol involves a tunable value for "the probability that an individual tag should respond."