| 摘要 |
The transmitter comprises means 1 for transmitting a message along a telephone line L1, L2 towards a monitoring station in response to an alarm delivered by at least one alarm contact 50, and means 3, 6 for power supply from the line current. It is characterised in that the alarm contact 50 and the power supply means 3, 6 are connected in series between two wires of the telephone line L1, L2. As long as the alarm contact is open, no energy is picked off by the transmitter. When the alarm contact is closed following an alarm, the transmitter acquires the line and picks off energy from the line only during setting up of a communication and transmission of a message. At the end of the communication, signalled by a hang-up signal from the monitoring station, the consumption of the transmitter again becomes nil. <IMAGE>
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