A protective guard prevents undesired access to a wall-mounted electrical interface such as an electrical switch or outlet, particularly by small children. The protective guard includes a baseplate, cover and spring-biased latch. The baseplate is mounted to the wall and contains at least one opening to expose the electrical interface. The cover slidably attaches to the baseplate for sliding movement between a closed position that blocks access to the electrical interface and an open position that exposes the electrical interface. The spring-biased latch is attached to the cover. The latch is actively spring-biased to a locked position that holds the cover in the closed position and has an unlocked position offset from the locked position which allows sliding movement of the cover to its open position to expose the electrical interface. Advantageously, exposing the electrical interface requires no additional parts or tools that should be procured, removed, stored, or could be misplaced. The required actions to expose the electrical interface are difficult to achieve by a small child while an adult has the required strength, motor skills, and cognitive abilities to easily and intuitively accomplish the necessary actions with a one-handed operation.