The PreonCube Signal Light (traffic light) is an optional extension to the PreonCubes. The traffic light locally displays a specific measured value in three different colored categories. The representation of the colors can deviate from the representation in the on-line range and react delayed. The traffic light can be used as an indicator when it makes sense to reduce the CO2 content in a room, for example, by ventilating and opening a window. Measuring ranges for the individual color categories can be configured.