A tire condition monitoring system is composed of a detector installed in each tire, a transmitter positioned in the vicinity of each tire, and a monitor communicating with the transmitters and the detectors. An initiation signal for initiating operation of the detector is wirelessly sent from the transmitter to the detector, using a low frequency, and the pressure and temperature data detected by the detector are wirelessly sent to the monitor, using a radio frequency. A vehicle identification code differentiating the vehicle from other vehicles may be included in the initiation signal to avoid confusion with signals wirelessly sent from other vehicles. The detector is operated only when the tire condition data from that detector are required to minimize power consumption in the detector.