Electronic identification system

An identification system for use in a retail store, comprising:

• (a) a plurality of transponders attached to retail goods, each of said transponders including means for responding to an interrogation signal by transmitting a response signal representing information stored in the respective transponder, each transponder being capable of operating in one of two modes, a first mode in which the response signal is at a first power level and a second mode in which the response signal is at a second, lower power level greater than zero, means for initially setting each transponder in the first mode, and means for switching from the first mode to the second mode in response to a mode switching signal, and wherein the information stored in each transponder is obtainable from the respective response signal irrespective of the power thereof being at the first or second level;
• (b) a checkout station, including means for generating said interrogation signal and means for detecting said response signal at said first power level, and means for generating said mode switching signal for subsequently switching said transponders into said second mode;
• (c) an anti-theft gate, including respective means for generating said interrogation signal, and means for detecting said response signal at said first power level but incapable of detecting said response signal at said second power level;
• and
• (d) a service station, including respective means for generating said interrogation signal, and means for detecting said response signal at said second power level as well as at said first power level and thereby obtaining the stored information from transponders on goods that have previously been passed through a said checkout station and switched to said second mode.

A method of identifying goods in a retail store, the method comprising:

• (a) tagging said goods with a plurality of transponders attached to said goods, each of said transponders initially being set to a first mode of operation in which each of said transponders transmits a response signal representing information stored in the respective transponder at a first predetermined power level in response to an interrogation signal,
• (b) at a checkout station interrogating said transponders with said interrogation signal to obtain a said response signal from each transponder, and switching each of said transponders into a second mode of operation, in which said response signal represents the information stored in the respective transponder but is reduced to a second power level, greater than zero and lower than said first power level;
• (c) at an anti-theft gate interrogating said transponders with said interrogation signal, detecting response signals from said transponders at said first power level and ignoring response signals from said transponders at said second power level, thereby detecting any goods that have not passed through said checkout station while ignoring goods that have passed through said checkout station;
• and
• (d) at a service station interrogating said transponders with said interrogation signal and detecting response signals from said transponders at said second power level as well as at said first power level, thereby being able to detect the stored information from transponders on goods which have previously passed through a said checkout station and been switched to said second mode.