Security alarm system

Claim 1

A security alarm system for watching emergency situations in a predetermined guard area comprising: a plurality of sensors for detecting the emergencies; a transmitter-receiver for a guard area connected to said sensors and having a battery power source; a repeater associated with said transmitter-receiver through radio; a security controller connected to said repeater; and a central station connected to said security controller using a transmission line and giving a guard command to an operator on the basis of emergency or ordinary data transmitted from said security controller; means for providing a pulsating voltage from said power source for the guard area such that a predetermined pulsating voltage is applied from said battery power source to said transmitter-receiver under ordingary conditions, a predetermined voltage having a longer term than a period of said pulsating voltage is applied to a receiving section of said transmitter-receiver in response to a watch signal transmitted from said security controller via said repeater before transmitting a guard mode signal from said security controller and a predetermined voltage having a longer term than the said pulsating voltage is applied to a transmitting section of said transmitter-receiver in response to an emergency signal transmitted from said sensors at emergencies, or in response to said guard mode signal transmitted from said security controller via said repeater; said repeater stores the emergency and ordinary data transmitted from said transmitter-receiver temporarily; and said security controller reads out these data stored in said repeater, discriminates emergency or ordinary data, and transmits emergency data and guard mode signal to said central station.