Means for recovering tamper evidence in RFID tags regardless of the power supply to the chip or reconnection of the tamper loop

An RFID tag which indicates that a tamper event has occurred includes a memory cell 1 connected to a conductive loop 6 by pins 12. The memory cell has a memory status set to '1' and contains a charge 2 which dissipates via the conductive loop 6 as a result of a tamper event. When the charge dissipates the memory status changes to '0'. Upon being interrogated by a reader, the tag sends memory status information to the reader thus indicating whether the tag has been tampered with. Preferably the conductive loop 6 includes a switch 5 which is closed when the tag is tampered with, causing dissipation of the memory cell charge. Alternatively, the conductive loop may be a closed circuit (not shown) which is opened as a result of tampering. A diode 4 prevents the memory cell from being reset by reconnecting or repairing the tamper circuit. A diode 9 prevents the cell from discharging when the voltage from the power supply 3 falls below a useful level. The tag may be used to indicate when the contents of a bottle have been tampered with.