Remote monitoring system

Claim 1

A remote monitoring system comprising: a monitoring station, a plurality of subscriber telephone sets each having transmit-receive means and a hook-switch for connecting said transmit-receive means to an individual telephone line, at least one concentrator to which said telephone lines from the subscriber telephone sets are connected, said concentrator being connected to the monitoring station through a signalling line and a conversation line, said concentrator comprising, for each of said telephone lines connected thereto, a signal generator means for generating a respective identification signal, first switching means arranged for connecting the signal generator means to the signalling line in response to an alarm signal from the subscriber telephone set, and second switching means arranged for connecting the respective telephone line to the conversation line in response to a control signal from the monitoring station; and each subscriber telephone set further comprising third switching means connected in parallel with said hook-switch, control device means responsive to external excitation for actuating said second switching means to short circuit the hook-switch and thereby put the telephone set in the off-hook condition without the hook-switch having been manually actuated, fourth switching means connected in series between the hook-switch and the telephone line, said fourth switching means normally closed, and signal receiver means adapted to produce a control signal for actuating said fourth switching means in response to an excitation signal from a remote sender unit, thereby to disconnect the subscriber telephone set from the telephone during a short time and transmit an alarm signal.