A vehicle occupant sensing system adapted for detecting a condition of a vehicle seat assembly that includes at least one emitter and at least one sensor disposed in spaced relationship to the emitter. The sensor is operable to detect relative distance to the emitter to thereby detect the condition of the vehicle seat assembly. The vehicle occupant sensing system also includes at least one sensor assembly with a base and an upper slide member slidingly supported for movement toward and away from the base. The upper slide member includes an exterior surface that is continuous to thereby block contaminants from entering the sensor assembly. Also, at least one of the emitter and the sensor is supported by the upper slide member. The vehicle occupant sensing system may be employed in a vehicle seat to detect a condition of the vehicle seat.