Abstract: In order also to allow the detection, for example, of condensation of the inner side of an interface (window) using motor-vehicle rain sensors that exploit the interference, at a window wetted with moisture, with total reflection of light irradiated by a transmitter, several sensors are proposed that are sufficiently variable in terms of configuration and function that they contain, without complex adaptation actions, an implementable possibility for selectable inside/outside detection simultaneously with good discrimination between outside and inside wetting.