SHOPLIFTING PREVENTION SYSTEM AND RESONANCE TAG TO BE USED FOR SAME SYSTEM

PROBLEM TO BE SOLVED: To provide a reliable shoplifting prevention system and a resonance tag to be used for the system. SOLUTION: A resonance tag 20 to be attached to merchandise comprises a resonance circuit constituted of a coil part having an inductance L and serially arranged two capacitor parts having the same electrostatic capacities C1 and C2. In this case, the resonance frequency f of the resonance circuit is turned to be a frequency f0 when the two capacitor parts are both provided with functions, and turned to be a frequency f1 when the function of any one capacitor part is invalidated. Also, a detection device is set so that that the resonance tag 20 having the resonance frequency f0 can be detected. Then, while merchandise is displayed in a store, the resonance frequency f of the resonance tag 20 can be turned to be the frequency f0, and when the merchandise is purchased by a guest, the two capacitor parts are short-circuited by a short-circuiting device at a register so that a resonance circuit can be canceled. COPYRIGHT: (C)2005,JPO&NCIPI