Abstract: An apparatus for preventing unauthorized use of machinery having an internal combustion engine (such as a motor vehicle) comprises an interruption subcomponent (46) for controlling flow of electrical current to an electrical ignition system (18) by allowing electrical current to flow from a power supply (10) to the electrical ignition system when the internal combustion engine is started, and thereby allowing the engine to run, and for interrupting this flow in response to an operator preforming an activity for further operating the machine (such as applying brakes or shifting gears). The apparatus also includes an arming subcomponent (48) for arming the interruption subcomponent (46) in response to the engine being started and disarming the interruption subcomponent in response to a manual manipulation of a switch (42, 44) of the arming subcomponent. In the described embodiment, the interruption and arming subcomponents respectively include interruption and arming solenoid switches.