A telemetry unit. (100) is provided for mounting inside a pneumatic tyre. The unit (100) includes a piezoelectric power generator for supplying power to the unit (100). A piezoelectric element (114) is supported in a housing (112) with an actuator 136 arranged for contact with the element (114), to deflect the element (114) in response to external forces acting on the actuator (136) during rotation of the tyre. For every rotation of the tyre, cyclic pulses of electrical charge are generated by the deflection of the element (114). The charge, is stored and utilised under a power consumption protocol to operate pressure and temperature sensors and to transmit data from the unit (100). The telemetry circuitry is mounted for movement with the actuator (136) and therefore contributes to the actuating mass acting on the clement (114).
