Adapter cards generally have a metal bracket at one end. The adapter card attaches to an adapter card slot of a computer system by fastening the bracket to a connector on the computer system. Conventionally, the bracket is fastened to the connector using a screw. It has been discovered that an electrically-conductive flip-down retainer advantageously functions as an improved fastener to secure the adapter card to the connector. The electrically-conductive flip-down retainer is a single structure that performs the combined functions of an electrical switch and a mechanical fastener. The electrically-conductive flip-down retainer includes electrical contacts that form a closed circuit when the bracket is fastened to the connector and an open circuit when the bracket is not fastened. The electrical contacts are connected to conductors extending to a controller. The controller monitors the status of the electrical switch of the electrically-conductive flip-down retainer and controls application of power to the adapter card slot, typically under control of an operating system. The controller terminates power to the adapter card slot when the electrically-conductive flip-down retainer is unfastened, indicating that the adapter card is disengaged from the adapter card slot. The controller restores power to the adapter card slot when the electrically-conductive flip-down retainer is fastened, indicating the adapter card is engaged with the adapter card slot.