Alarm system

Claim 1

AN ALARM SYSTEM COMPRISING IN COMBINATION FIRST AND SECOND STATIONS AND AN ELECTRICAL TRANSMISSION LINE COUPLED THEREBETWEEN, SAID FIRST STATION INCLUDING ACOUSTIC TRANSDUCER MEANS FOR PRODUCING AN A.C. ELECTRICAL SIGNAL OUTPUT IN RESPONSE TO ACOUSTIC VIBRATIONS, AMPLIFIER MEANS COUPLED TO SAID ACOUSTIC TRANDUCER AND TO ONE END OF SAID TRANSMISSION LINE, SAID AMPLIFIER MEANS BEING RESPONSIVE TO AN A.C. SIGNAL OUTPUT FROM SAID TRANSDUCER FOR SUPPLYING SAID A.C. ELECTRICAL SIGNAL OUTPUT TO SAID LINE, AND A FIRST D.C. POWER SUPPLY MEANS COUPLED TO SAID FIRST AMPLIFIRST D.C. POWER SUPPLY MEANS COUPLED TO SAID FIRST AMPLIOF SAID TRANSMISSION LINE FOR PLACING A FIRST LEVEL OF D.C. VOLTAGE SIGNAL UPON SAID LINE, SAID SECOND STATION INCLUDING ENERGIZABLE AUDIO REPRODUCING MEANS FOR PRODUCING AN AUDIBLE OUTPUT FROM SAID A.C. ELECTRICAL SIGNAL OUTPUT AS RECEIVED OVER SAID LINE, SECOND D.C. POWER SUPPLY MEANS HAVING A D.C. VOLTAGE LEVEL, SWITCHING MEANS FOR CONNECTING SAID SECOND D.C. POWER SUPPLY MEANS WITH SAID ENERGIZABLE AUDIO REPRODUCING MEANS, AND COMPARISON MEANS COUPLED BETWEEN THE OTHER END OF SAID TRANSMISSION LINE AND SAID SECOND D.C. POWER SUPPLY MEANS FOR PRODUCING AN OUTPUT IN RESPONSE TO VARIATION IN THE COMPARATIVE LEVEL OF SIGNALS RECEIVED BY SAID COMPARISON MEANS FROM SAID TRANSMISSION LINE AND SAID D.C. VOLTAGE LEVEL OF SAID SECOND D.C. POWER SUPPLY MEANS RESPECTIVELY, SAID SWITCHING MEANS BEING COUPLED TO SAID COMPARISON MEANS FOR OPERATION OF SAID SWITCHING MEANS TO CONNECT SAID SECOND POWER SUPPLY MEANS WITH SAID ENERGIZABLE AUDIO REPRODUCING MEANS IN RESPONSE TO A PREDETERMINED OUTPUT FROM SAID COMPARISON MEANS.