Alarm system

Claim 1

AN ALARM SYSTEM COMPRISING A FIRST UNIT HAVING MEANS FOR DETECTING A DISTURBANCE, AN ALARM UNIT REMOTE FROM THE FIRST UNIT, THE ALARM UNIT INCLUDING A BATTERY, AN ANNUNCIATOR, AND SWITCHING MEANS OPERABLE TO CONNECT THE ANNUNCIATOR ACROSS THE BATTERY IN ORDER TO OPERATE THE ANUNCIATOR, A LINE CONNECTING THE FIRST UNIT AND THE ALARM UNIT, A DIRECT CURENT POWER SUPPLY CONNECTED ACROSS THE LINE FOR POWERING THE FIRST UNIT AND SUPPLYING CHARGING CURRENT OVER THE LINE TO THE BATTERY, NON-RECTIFYING RESISTIVE MEANS CONNECTED IN SERIES BETWEEN THE LINE AND THE BATTERY TO CONDUCT THE CHARGING CURRENT WHEREBY THE CHARGING CURRENT FLOWS THROUGH THE RESISTIVE MEANS AND, IN THE EVENT OF A FAILURE OF THE POWER SUPPLY, CURRENT FLOWS FROM THE BATTERY THROUGH THE RESISTIVE MEANS AND THE LINE TO POWER THE FIRST UNIT, THE RESISTIVE MEANS HAVING NORMALLY A RELATIVELY LOW RESISTANCE, BEING RELATIVELY UNHEATED BY THE CHARGING CURRENT, BEING NON-FUSIBLE BY THE CURRENT THAT FLOW THROUGH IT FROM THE BATTERY IN THE EVENT OF A SHORT CIRCUIT CONDITION ACROSS THE LINE BUT BEING RAPIDLY HEATED BY THE LAST MENTIONED CURRENT AND HAVING A HIGH POSITIVE TEMPERTURE COEFFICIENT OF RESISTANCE WHEREBY THE RESISTANCE OF THE RESISTIVE MEANS RISES RAPIDLY IN THE EVENT OF SUCH A SHORT CIRCUIT CONDITION TO PREVENT RAPID DISCHARGE OF THE BATTERY, AND MEANS RESPONSIVE TO A SHORT CIRCUIT CONDITION ACROSS THE LINE TO OPERATE THE SWITCHING MEANS TO CONNECT THE ANNUCIATOR ACROSS THE BATTERY.