A position sensor system is provided at a slidable vehicle seat for sensing seat position in zones and facilitating controlling of the operation of a vehicle passenger restraint device according to a position of the vehicle seat relative to the vehicle passenger restraint device. The vehicle seat includes a pair of substantially parallel slide rail mechanisms which comprise upper rail members and lower rail members mounted to a floor of a vehicle, the upper rail members being attached to lower portions of the vehicle seat and supported to the lower rail members so as to be movable along the lower rail members, so that the vehicle seat can be moved along the lower rail members. The upper rail members and the lower rail members are combined with each other, to thereby define inner spaces. The position sensor system is mounted within at least one of the inner spaces.