Fire alarming system

Claim 1

A fire alarm system comprising a plurality of fire detecting units for sensing heat or smoke, a receiving station including a direct current power supply, a pair of conductors connected at one end to said power supply, connections between each detecting unit and said conductors, each of said units including an AC generating device having a preselected frequency, heat or smoke detecting means electrically coupled with said generating means and with said conductors, and means including DC blocking means coupling said generator to said conductors whereby actuation of one of said detecting means at least partially shunts said conductors to increase the flow of current therethrough and causes an AC signal to be applied to said conductors, and said receiving means includes means responsive to an increase in current in said conductors to produce an alarm, frequency discriminating means responsive to said AC signals and a plurality of indicating means interconnected with said discriminating means, each of said indicating means being selectively activated by said discriminating means upon activation of one of said detecting units to identify the location of the detecting unit producing an alarm.