Abstract: A tire position determination system provided in a vehicle including a first tire and a second tire includes an initiator that transmits a command signal, a first detector attached to the first tire, a second detector attached to the second tire, and a monitoring unit. A distance between the first tire and the initiator is equal to or shorter than a distance between the second tire and the initiator. Each of the first detector and the second detector includes an acceleration sensor. A detection signal includes a detection value from the acceleration sensor. The monitoring unit performs determination processing for determining a position of the first tire and a position of the second tire based on positional relation between the detector and the initiator estimated from the detection value from the acceleration sensor.

Abstract: A vehicle-mounted system provided in a vehicle including a tire includes a detector attached to the tire, the detector transmitting a detection signal, and a monitoring unit that determines a position of the tire based on a plurality of detection signals received from the detector. The detector determines a direction of revolution of the tire, and when the detector determines that the direction of revolution of the tire has changed, it switches a frequency of transmission of the detection signal from a first frequency to a second frequency higher than the first frequency.