Abstract: A security device for motor vehicles and other d.c. electrical systems responsive to use of the system wherein an alarm or other security element is connected across the source, a relay has its switch connected to the alarm element and its coil connected to a switch maintained open in the stand-by condition responsive to maintained voltage of the d.c. source or battery, the switch closing responsive to lowered d.c. voltage to energize the relay coil and close the relay switch to actuate the alarm element, and delay means controlling the time required by the relay coil switch to assume its open stand-by condition.

Abstract: An electric switch magnetically activatable including a Hall Effect sensor with a permanent magnet fixed on one side of the sensor and magnetic shielding interposed between the sensor and fixed magnet to direct flux away from the sensor, such that an operating magnet upon movement toward and away from the other side of the sensor cooperates with fixed magnet to produce an increased magnetic field through the sensor to activate the latter.

Abstract: An ignition circuit tester including a pick-up coil assembly for inductive coupling with and location closely along a circuit element to be tested, an amplifier circuit for amplifying a signal picked up by the coil assembly, and a meter to indicate the signal.