PURPOSE: To provide a security system using a resonant label which can be fixed to every merchandise and becomes valid only at the time of desiring to make it in an operated state on the other hand.

CONSTITUTION: A manufacturer fits the resonant labels to all the merchandise (300). The resonant label is provided with plural circuit bodies responding to different frequencies. At the time of receiving merchandise, one circuit body of of the merchandise is invalidated (302). The resonant label comes into an active state and an exit sensor outputs an alarm (310). The resonant label in the active state is returned into an inactive state by the invalidating of the circuit body of the other side (304). This resonant label does not issue an alarm (308). On the other hand, the resonant label no circuit body of which is invalidated does not output an alarm.