The Homematic IP contact interface for flush mounting - single allows for the easy integration of a conventional switch, button, or contact into the Homematic IP smart home system. In combination with Homematic IP actuators, existing lamps or blinds can be intelligently controlled and flexibly automated via radio through the Homematic IP system. Alternatively, the contact interface can also be used to activate or deactivate eco mode in conjunction with Homematic IP room climate products. Installation is straightforward, as only the supplied wires of the contact interface need to be connected, and thanks to the long-lasting lithium battery power supply, no external power source is required for operation. After successful installation and commissioning via the Homematic IP Access Point, a CCU2/CCU3 central unit, or a suitable partner solution, the respective switch state can be determined and controlled individually. Due to its low installation depth of around 12 mm, the flat flush-mounted interface fits even in standard flush-mounted boxes and can be placed directly behind the already installed switch insert, which can then be reused.