Abstract: Apparatus for causing a starting motor interlock switch to be activated when the vehicle engine ignition is running, the vehicle having an electrical battery associated with the engine, and the running of the engine causing impulse signals to appear at an inductively coupled sensing element. The apparatus has an electrical circuit which converts the incoming impulses to a DC signal indicating an engine running condition. The invention senses when the ignition circuit of an engine has operated in excess of a predetermined time interval. Having sensed such operation, the unit latches into a position which open-circuits a relay (interlock) thereby causing the starting motor system of the vehicle to become disabled. When the ignition source shuts off, the unit latches into a position which re-enables the starting motor circuit after a predetermined time interval.