Tire condition monitoring system

The invention relates to a tyre condition monitoring system, to a sensor device, a wheel transmitter unit and a transducer for use therewith, to a method of calibration, and to a transceiver circuit. A tire condition monitoring system () comprises a wheel transmitter unit () for each wheel of a vehicle. The transmitter unit is mountable in the wheel and has sensors () for sensing pressure and temperature in and rotation of the wheel. Signals from the sensors are processed by a processor () to produce data which is transmitted via a radio frequency transmitter (). The data is transmitted with data representing a unit identity code. Transmitted data is received by a receiver unit () where it is analyzed to determine the condition of the tire. The receiver unit includes a user operable input for setting threshold limits for the temperature and/or pressure such that if a threshold is passed an alarm is sounded. Each wheel transmitter unit includes a power supply and is arranged so that power is only applied during the sensing and transmission of data. Intervals between transmissions of data can be varied depending on whether rotation of the wheel has been sensed.