A seat assembly is provided that can be sat upon by an occupant that detects the weight of the occupant. The seat assembly includes a seat cushion, a rotary sensor, and a linkage having a tip. The seat cushion deforms in response to the weight. The rotary sensor has a shaft that rotates about an axis and has an electrical output that is proportional to the angle of rotation of the shaft. The linkage underlies the seat surface and connects the seat surface to the shaft of the rotary sensor. As weight is placed on the seat the seat cushion deforms in response to the weight moving the tip and the linkage. The movement of the linkage rotates the shaft, which in turn, provides an electrical output that is proportional to the weight.