can send a radio signal to the tag 10 through the antenna 31 and receiver 33 in response to receipt of this signal the tag 10 uses the transmitter circuit 32 and antenna 31 to send a radio signal that indicates the state of the low battery flag and also the number in the counter after receiving this type of signal from each of a number of different tags the not illustrated reader can determine which tags need a battery replacement and also the relative degree of urgency for replacing the battery in each of these tags the reader can then prioritize the order in which a technician is instructed to replace the discharged batteries in respective different tags from block 133 the program proceeds to block 138 as discussed above the control circuit 12 can operate in three different operational modes including a receive mode a transmit mode and a standby mode in block 138 the program determines which of these three operational modes is the current operational mode of the control circuit 12 and then proceeds to a corresponding one of three blocks shown at 141 142 and 143 in particular if the control circuit 12 is currently in the receive mode the program proceeds from block 138 to block 141 where the program updates a receive accumulator which is one of the accumulators that was cleared in block 103 of fig4 the receive accumulator contains a number representing the cumulative amount of.