| 摘要 |
PROBLEM TO BE SOLVED: To perform data communication between a center device and a plurality of monitoring terminal units by a single telephone line, and to sufficiently and quickly cope with even emergency. SOLUTION: The center device 2 sends a calling-out signal to the whole monitoring terminal units 5A to 5C via the telephone line 3 and an exchange 4, and also transmits a car number related to, for example, the monitoring terminal unit 5A after passing preset time. The monitoring terminal unit 5A performs the data communication with the center device 2 by unhooking a hook when recognizing this car number. While, the monitoring terminal devices 5B and 5C open telephone lines 3a and 3b by unhooking the hook when recognizing this car number.
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