Abstract: An electrical circuit, the starting circuit for a motor vehicle for example, is selectively enabled by a control circuit which includes a magnetic field responsive switching device. Proper positioning of a magnet which provides a field of the appropriate polarity and strength relative to the switching device results in the energization of a relay which has contacts connected in series with the circuit being controlled. In the motor vehicle application, operation of the ignition switch within a pre-determined time subsequent to removal of the magnet will latch the relay in the energized state.