| 摘要 |
The method involves stopping transmission of identification messages from an alarm unit (10a,10b,10c) if an identification message does not arrive at the identification unit (30). The identification unit sends a control message to the alarm unit if an identification message is not received at one of predetermined time points. If a receipt for the control message is not received in a predetermined time period an alarm is released in a central control unit (20) by the identification unit. The alarm units are placed at positions to be monitored and are connected to the central control unit via a public telephone network (40) and the identification unit. |
