| 摘要 |
PROBLEM TO BE SOLVED: To sufficiently ensure the security of a monitored area without declining such a convenience as a reduction in communication expenses. SOLUTION: A monitoring center 30 transmits a fixed-time signal on a predetermined schedule to a plurality of monitoring centers 20 which monitor using a data communication band 1a. Each of the monitoring centers 20 which have received the fixed-time signal transmits a confirmation signal indicating the receipt of the confirmation signal to the monitoring center 30. If the monitoring center 30 does not receive a confirmation signal from the monitoring devices 20 to which the fixed-time signal has been sent within a predetermined period of time after transmitting the fixed-time signal, the monitoring center 30 transmits a confirmation signal again using a voice communication band 1b. COPYRIGHT: (C)2005,JPO&NCIPI
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