A plug-in device system has a closure unit blocking access to a first plug-in device element, for example a socket. The closure unit includes a rotary bezel which is coupled via a coupling to at least one shutter such that the rotation of the bezel effects a movement of the shutter from a closed position in an open position. Preferably, a locking assembly is additionally provided, which blocks movement of the rotary bezel and/or shutter in the closed position as long as no pressure is applied to the shutter. In addition, a safety device can be provided, which prevents the shutter from opening when a direct force is applied.