| 摘要 |
PROBLEM TO BE SOLVED: To provide a theft preventing system by which the display range of a merchandise is enlarged and also alarm is prevented from being issued without reason. SOLUTION: The system is constituted in such a way that radio wave signals with mutually different frequencies are respectively transmitted by plurally arranged transmission antennas 3 and 4, an alarm area Z where the radio wave signals with the whole frequencies coexist is formed, alarm is issued by giving an alarm command to an alarm means when it is judged that an article monitoring device exists in the alarm area Z by a controller constituting the device based on the reception of the whole-frequency radio wave signals and the alarm area Z for issuing alarm is narrowed and limited as desired.
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