In a base element of a waveguide for a detector system at least one portion of radiation passing via the front side and impinging on a diffractive element in the display region is deflected via the diffractive element according to the selection region. The deflected portion is propagated as coupled-in radiation via reflection to an out-coupling region and impinges on the associated out-coupling section of the out-coupling region. The portion of radiation coupled out by an out-coupling section impinges on an associated sensor section of the sensor unit, which continuously measures the intensity of the impinging radiation and supplies the control unit, wherein, according to a change of intensity, which is dependent on positioning an object in front of the front side of the base element and in front of a selection region of the display region, the control unit determines whether the one selection region has been selected.