A security device for locking the cable of a bonnet lock of a car comprising a housing with cable inlets. The inner core of the cable is secured to a cable engaging member which is movable within the housing on a pivot member about a pivot pin. A solenoid spindle mounted on the pivot member engages a bracket mounted on the housing to prevent pivotal movement of the cable engaging member. A compression spring biases the spindle into engagement with the bracket on de-energizing of the solenoid to lock the cable.