IMPIANTO PER RIVELARE ANORMALITA'NELLA PRESSIONE INTERNA DI UN PNEUMATICO

A detection system for detecting abnormality in the internal air pressure of a tire of a motor vehicle produces an alarm upon detection of an abnormal change in the air pressure of the tire. The system comprises a first device which is disposed at a wheel (or a rotating part) of the motor vehicle and has an abnormal pressure detecting means using a crystal resonator and an antenna for sending out detection information in the air; and a second device which is disposed for example in the vicinity of a driver's seat (or at a non-rotating part) and has a transmitter/receiver arrangement provided with an antenna. The crystal resonator is driven by an exciting energy sent out from the transmission part of the transmitter/receiver. Immediately after ceasing of the exciting energy from being sent out, a signal is discharged from the crystal resonator by an oscillatory energy accumulated at the above stated resonator and is received by the receiving part of the transmitter/receiver to show abnormality in the internal pressure of the tire if there is any. The crystal resonator is either used solely as information (abnormal decrease of air pressure in the tire) transmitting means in combination with an abnormality detecting switch (a pressure responsive element) or used also for abnormal pressure detection as well as for transmission of the information.