A weight based occupant detection device that includes a weight sensing device installed in a vehicle seat in a manner effective to sense weight on a seating surface. The weight sensing device is configured to output a weight signal indicative of an occupant weight of a seat occupant residing on the vehicle seat. The occupant detection device also includes a seat orientation angle sensing device that is configured to output an orientation angle signal indicative of a seat orientation angle. The occupant detection device may also include an accelerometer for sensing vertical acceleration of the vehicle seat, and a seat backrest angle device for measuring the angle of the seat backrest. The occupant detection device compensates a signal from the weight sensing device for errors caused by seat orientation, seat vertical acceleration and seat backrest angle.