A transmitter includes a condition detecting section, which detects a condition of a tire, a memory section, which stores identification information, a transmitting section, which transmits a data signal, a trigger receiving section, which receives a trigger signal transmitted from a trigger device, and a controlling section. When the trigger receiving section receives the trigger signal, the controlling section generates data corresponding to the trigger signal and causes the transmitting section to transmit the data signal, which includes the generated data. The controlling section generates encrypted data when the trigger receiving section receives a trigger signal of unmodulated waves. The controlling section generates non-encrypted data that includes the identification information when the trigger receiving section receives a trigger signal of modulated waves.