Abstract: To prevent inaccurate weighing on a platform scale in the event that a driver of a motor vehicle has purposefully or inadvertently positioned his vehicle with one or more of the vehicle wheels located off of the weighing platform, the platform scale is provided with an alarm system which comprises a weight responsive mat switch located in the roadbed along the perimeter of the weighing platform, a signal located in the proximity of the scale operator, and means interconnecting the mat switch and the signal for actuating the signal and alerting the scale operator in response to one or more wheels of the motor vehicle coming into engagement with the mat switch.