System for detecting intruders

Claim 1

AN INTRUDER DETECTION SYSTEM COMPRISING AN ELECTRICAL ELEMENT RESPONSIVE TO LIGHT AND OTHER RADIATIONS TO CHANGE ELECTRICAL VALUES THEREOF AND HAVING A SURFACE EXPOSED TO AMBIENT LIGHT, A PARTITION DIVIDING SAID SURFACE INTO TWO ISOLATED PORTIONS, FIRST AND SECOND RADIATIONS GENERATING DEVICES AT THE RESPECTIVE SIDES OF SAID PARTITION FOR EXPOSING SAID SURFACE PORTIONS TO RADIATIONS FROM SAID DEVICES, A SOURCE OF A.C., REACTANCE MEANS CONNECTED IN SERIES WITH SAID ELEMENT ACROSS SAID A.C. SOURCE, A FIRST DIODE CONNECTED IN SERIES WITH SAID FIRST DEVICE ACROSS SAID A.C. SOURCE, AND ARRANGED TO CONDUCT IN ONE DIRECTION OF CURRENT FLOW, A SECOND, DIODE CONNECTED IN SERIES WITH SAID SECOND DEVICE ACROSS SAID A.C. SOURCE AND ARRANGED TO CONDUCT IN THE OPPOSITE DIRECTION OF CURRENT FLOW WHEREBY SAID DEVICES ARE ALTERNATELY ENERGIZED TO ALTERNATELY EXPOSE SAID SURFACE PORTIONS TO AN EQUAL HIGHER AND LOWER RADIATION INTENSITY, SAID REACTANCE MEANS HAVING AN OUTPUT UPON BEING CHARGED UNEQUALLY AT OPPOSITE SIDES IN SEQUENCE DUE TO PRESENCE OF AN INTRUDER, AND MEANS CONNECTED ACROSS SAID RECTANCE MEANS RESPONSIVE TO THE OUTPUT OF SAID REACTANCE MEANS FOR RENDERING AN ALARM.