A device for controlling an optical recognition unit with the help of a capacitive filling level measurement in liquid containers having a sensor with a measuring electrode, a conductive base plate suitable for arranging at least one liquid container or a carrier unit having at least one receptacle for receiving a liquid container, a sensor electronics unit that is connected to the measuring electrode and the base plate adapted to determine a capacitance between the measuring electrode and base plate, an evaluation unit, and a control unit for controlling the optical recognition unit, is disclosed.