A lock for a vehicle-ignition circuit. The lock includes a sleeve, a cylinder rotatably coupled within the sleeve and having a keyway therein that receives a key that allows the cylinder to rotate, and a sensor including a pair of spaced-apart switch contacts and a movable electrically-conductive body. The body is movable between a first position where the body is located away from at least one of the switch contacts and a second position where the body contacts both of the switch contacts. The sensor defines a region in which the sensor is responsive to the effects of an actuator, and is coupled to the sleeve so that the region is located within the rotation of the cylinder and is in an orientation in which the body is located in the first position in the absence of the actuator within the region.