A tire pressure monitor enables the TPMS (Tire Pressure Monitoring System) in a tire to detect and send a tire pressure signal from an air faucet to the outer side of the wheel rim by an antenna connecting line, and uses an insulation sleeve to isolate an electrical transmission between the air faucet and an external air faucet so that the whole external air faucet becomes an insulating and independent transmitting antenna which can be unaffected by the serious shield from the wheel rim or steel wire annulus. Therefore, the tire pressure can be measured directly by the tire pressure detector inside of the tire and the transmitting signal can be sent accurately to the receiver in the vehicle in order to enhance the reliability of measuring tire pressure and driving safety.