A tire pressure monitoring system (TPMS) sensor assembly 1 has a housing 2, a pressure sensor mounted in the housing 2 and an antenna 3 connected to the sensor and extending exteriorly of the housing 2 for effecting wireless communication between the sensor and a remote module. The antenna 3 is moveable between a folded position in which it extends around at least a part of the housing 2 so as to lie substantially in the plane of the housing 2 and an erect position in which it upstands from the housing 2 so as, in use, to extend into the inflation area formed between a wheel and tire. The antenna 3 is biased towards its erect position, and further includes a releasable restraining strap 7 for restraining the antenna 3 in its folded position.