A wheel-mounted tire pressure sensor employs a Bourdon tube which deforms in relation to tire pressure to drive a pivotal arm. Opposite ends of the arm support magnets which can close reed switches arrayed around the path of travel of the magnets. The reed switches are connected to passive resonators...http://www.google.es/patents/US4529961?utm_source=gb-gplus-sharePatente US4529961 - Tire pressure sensor and sensing system
