| 摘要 |
PROBLEM TO BE SOLVED: To prevent a cellular phone or the like from being illegally used due to a disguise of an electric field strength level by a repeater. SOLUTION: When it is determined that a user 15 carries a cellular phone 1 because an electric field strength level from a portable key 2 to the cellular phone 1 exceeds a threshold, an electric field strength level, which should be constant because a relative distance is unchangeable, between the cellular phone 1 and fixed communication equipment 3 being a fixed station provided in a store or the like is measured. When the electric field strength level increases, it is determined that the disguise of an electric field strength level by a radio wave repeater or the like is performed, and device functions are locked so as to prevent unauthorized speech communication and settlement function of the cellular phone from being executed or the like. COPYRIGHT: (C)2008,JPO&INPIT
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