A process and a device are provided for ascertaining the rotation of a liquid spray arm for a domestic appliance. Lighting means serves as a light transmitter and a photoreceiver serves as a light receiver. The lighting means and the photoreceiver are assigned a light-conducting element. At a first location of the light-conducting element, at least some light emitted from the lighting means is coupled to a path so that the light is guided in the light-conducting element by total reflection. At a second location of the light-conducting element that spaced apart from the first location in the direction of propagation of the light, the light guided in the light-conducting element is coupled out of the path so that the light is received by the photoreceiver. The intensity of the light received by the photoreceiver is evaluated by an evaluation circuit with respect to the rotation of the spray arm.