SYSTEM FOR TRANSMITTING ALARM INFORMATION OVER TELEPHONE LINES

摘要

An alarm system for transmitting alarm information via telephone lines has a plurality of alarm transmitters which are located at subscribers' premises and are adapted to transmit signals indicative of the state of alarms associated with the transmitters along telephone lines to associated receivers. The receivers are located at one or more local exchanges and the receivers at a local exchange are all connected to a local processor. The or each local processor is connected to a central processor which can direct alarm information to one of a number of terminal stations. The local processors continuously scan the outputs of the receivers. When a local processor detects a signal indicative of an alarm condition it transmits a signal coded with the subscriber identity and destination for the alarm information to the central processor which routes the alarm message to the appropriate terminal station. Each transmitter produces a carrier wave which is modulated with one or more other frequencies according to the state of the alarm being monitored. The local processor claimed herein has means for continuously scanning the outputs of receivers connected thereto, memory means for storing data indicative of alarm conditions sensed during the previous scanning sequence, means for comparing the condition of an alarm with its condition during the previous scanning sequence and means responsive to said comparing means detecting a change in the condition of an alarm for transmitting a signal indicative of said alarm and the destination of the signal to a central processor.