VEHICLE-MOUNTED SYSTEM

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.