A vehicle seat assembly for detecting a condition of the seat assembly. The vehicle seat assembly includes a seat cushion. The vehicle seat assembly also includes a vehicle occupant sensing system having a plurality of sensor assemblies. Each sensor assembly includes a base and an upper slide member. The upper slide member is supported for movement toward and away from the base in response to a condition of the seat cushion. Additionally, the vehicle seat assembly includes at least one seat cushion insert having a topside and an underside. The seat cushion insert is disposed between the seat cushion and the sensor assemblies, and the topside has at least one planar section.