Access control equipment and method for using the same

Access control equipment comprising:

• a plurality of transponders;
• and
• an interrogation unit having means for emitting interrogation signals and means for controlling said interrogation signals, said interrogation unit interrogating all said transponders within range of said interrogation unit;
• each of said plurality of transponders having means for receiving the interrogation signals, and means for storing an identity code different from that of other transponders, the identity code comprising a plurality of fields, each field holding information having a value selected from a plurality of possible values, wherein
• said means for controlling said interrogation signals causes said interrogation unit to simultaneously interrogate said transponders to determine the values of information held by said transponders in a first field, then to interrogate those transponders which have responded with the values they hold in the first field to determine the values which they hold in a second field, then to interrogate those transponders which have responded with the values they hold in the first and second fields to determine the values which they hold in a third field, and so on until all fields have been interrogated,
• said plurality of transponders each further comprising means for sending group reply signals to the interrogation unit, said group reply signals containing the value which is held by the transponder in the field being interrogated,
• wherein each interrogation after a first interrogation is based upon the group reply signals received from the plurality of transponders, and successive interrogations are narrowed such that only those transponders for which group reply signals have been received are further interrogated, said interrogation unit further comprising means for converting group reply signals received in response to interrogation signals interrogating all fields, into the identity codes of those transponders within range.