Patent ID: 6567501
Filing Date: 2003-05-20
Classification: H04M,H04Q

Abstract:
An alarm system comprising:a control and switching system; a network terminal at an area to be monitored; and a first connection between the network terminal and the control and switching system, the control and switching system is arranged to monitor the first connection between the control and switching system and the network terminal, wherein the first connection comprises: a power feed line for feeding power from the control and switching system to the network terminal, wherein the control and switching system is arranged to give an alarm to a pre-determined alarm monitoring system in response to detecting an increase of current over a predetermined threshold value in the power feed line, wherein the control and switching system is arranged to synchronized with the network terminal and comprises means for detecting a break off of the connection between the network terminal and the control and switching system by detecting loss of synchronization and the control system is arranged to give the alarm in response to detecting the loss of synchronization, wherein the alarm system further comprises: a sensor in the area to be monitored, which sensor is, at its one end, connected with the first connection via a closing switch for causing a short-circuit in said connection, which short-circuit is arranged to be detected in the control and switching system from one of an increase of current feeding into the said first connection, and an increase of current feeding into the said first connection and loss of synchronization, and wherein the control and switching system is a switching center of a telephone network, and said short-circuiting switch is connected between the control and switching system and the ISDN subscriber line network terminal.