A group of associated transponders are respectively attached to a plurality of objects, such as sensors or containers. Each transponder includes a memory, a transmitter, a receiver and a controller. The memory stores group data, which includes data related to the respective attached objects. The controller causes the transmitter to autonomously transmit a group interrogation signal and to transmit a response signal in response to receipt of a group interrogation signal from another transponder of the group. The response signal includes at least some of the stored group data. The receiver receives both the group interrogation signals and the response signals from the other transponders of the group. The controller controls the transmitter and receiver and causes the memory to store data related to the respective object to which the transponder is attached and to store the group data included in the received response signals.