Abstract: A tire pressure detector for motor vehicles which is to be fastened to a wheel rim comprises a pressure switch actuated by the air pressure in the tire for monitoring the tire pressure. The pressure switch includes a reference pressure chamber with an electrically conductive switching diaphragm which closes the chamber toward the tire and which cooperates with a contact pin of the reference pressure chamber and an electric oscillating circuit connected to the latter in the detector housing. The reference pressure chamber (23) is axially clamped between a supporting ring and a spacing ring of insulating material in the metallic detector housing by a radial collar, which is formed, so that an annular gap is formed between the collar and the inner wall of the detector housing.