Abstract: A tire pressure sensor for motor vehicles comprises a pressure switch which is actuated by the tire pressure for monitoring the tire pressure. The pressure switch has a reference pressure chamber which is closed in the direction of the tire by means of an electrically conducting diaphragm and carries a contact pin which is contacted by the middle area of the diaphragm in order to close an electric circuit when there is sufficient air pressure in the tire. In order to trigger an alarm signal during a leak in the reference pressure chamber a leakage check of the reference pressure chamber is realized in that an air gap is located between the contact pin and the middle area of the diaphragm when there is equal pressure on both sides of the diaphragm.