1. A THERMAL THRESHOLD RESPONSIVE DEVICE COMPRISING IN COMBINATION: A BODY OF PYROELECTRIC CERAMIC MATERIAL HAVING ELECTRODES IN ELECTRICAL CONTACT WITH OPPOSITE FACES THEREOF, SAID CERAMIC MATERIAL BEING OF THE TYPE WHICH IS POLARIZED TO ESTABLISH A DIFFERENCE OF POTENTIAL BETWEEN SAID ELECTRODES DEPENDENT UPON THE TEMPERATURE OF SAID BODY AND, UPON REACHING THE CURIE POINT OF SAID MATERIAL, SUDDENLY LOSES ITS POLARIZATION AND RELEASES A HIGH ELECTRICAL CHARGE AT SAID ELECTRODES; HOUSING MEANS ENCLOSING SAID BODY, SAID HOUSING MEANS INCLUDING WALLS FORMED OF THERMALLY INSULATING MATERIAL IN ORDER TO REGULAR AND DELAY THE ACTION OF EXTERNAL HEAT ON SAID BODY; MEANS CONNECTED TO SAID ELECTRODES CONSISTING OF A CLOSED PASSIVE ELECTRIC CIRCUIT INCLUDING A CURRENT RESPONSIVE MEMBER AND A CONDENSER OF SUBSTANTIAL CAPACITY WITH RESPECT TO THE CAPACITY OF SAID BODY AT THE CURIE TEMPERATURE THEREOF, SAID CONDENSER BEING SHUNT CONNECTED ACROSS SAID ELECTRODES, AND AT LEAST ONE SWITCH WITH AN EXTERNAL CONTROL CONNECTED IN SAID CIRCUIT BETWEEN SAID CURRENT RESPONSIVE MEMBER AND THE POINT OF CONNECTION OF SAID CONDENSER; AND MEANS FOR SUBJECTING SAID BODY TO A SOURCE OF HEAT TO VARY THE TEMPERATURE OF SAID BODY FROM A POINT BELOW THE CURIE POINT TO A TEMPERATURE ABOVE THE CURIE POINT; WHEREBY WHENEVER SAID BODY IS HEATED TO A TEMPERATURE WHICH EXCEEDS ITS FERROELECTRIC CURIE POINT, A SUDDEN CURRENT FLOWS IN SAID CIRCUIT TO ENERGIZE SAID CURRENT RESPONSIVE MEMBER.