A tire pressure monitoring apparatus (10,301) comprising: a body (20,220,302) comprising an enclosed internal volume (25,225,304,310); mounting means for mounting the apparatus to a tire valve, a valve in gaseous communication with the internal volume of the body for receiving a tire inflation device to allow inflation of the tire via the apparatus; and an enclosed pressure chamber (50,250), in gaseous communication with the mounting means, for receiving the internal pressure of a tire to which the apparatus is mounted, the chamber housing at least: a power source (52,152,252,314); a pressure sensor (54,154,254,313); and an antenna (56,156,256,312) for emitting a signal indicative of a pressure within the chamber; the power source, pressure sensor and antenna being at least partially encased in a binding material (60,295,315) to maintain their relative positions in the pressure chamber; characterised in that the mounting means comprises means for opening the tire valve to allow gaseous communication between the internal volume of the tire and the internal volume of the body; and in that the apparatus comprises control circuitry (54,154,254,313) housed in the pressure chamber, the control circuitry comprising the pressure sensor, and the control circuitry being configured to activate once it is subjected to a predetermined pressure and thereafter to control the antenna to emit the signal wherein the control circuitry is configured to control the antenna to produce periodic signals indicative of at least the pressure within the chamber. a body (20,220,302) comprising an enclosed internal volume (25,225,304,310); mounting means for mounting the apparatus to a tire valve, a valve in gaseous communication with the internal volume of the body for receiving a tire inflation device to allow inflation of the tire via the apparatus; and an enclosed pressure chamber (50,250), in gaseous communication with the mounting means, for receiving the internal pressure of a tire to which the apparatus is mounted, the chamber housing at least: a power source (52,152,252,314); a pressure sensor (54,154,254,313); and an antenna (56,156,256,312) for emitting a signal indicative of a pressure within the chamber; a power source (52,152,252,314); a pressure sensor (54,154,254,313); and an antenna (56,156,256,312) for emitting a signal indicative of a pressure within the chamber; the power source, pressure sensor and antenna being at least partially encased in a binding material (60,295,315) to maintain their relative positions in the pressure chamber; characterised in that the mounting means comprises means for opening the tire valve to allow gaseous communication between the internal volume of the tire and the internal volume of the body; and in that the apparatus comprises control circuitry (54,154,254,313) housed in the pressure chamber, the control circuitry comprising the pressure sensor, and the control circuitry being configured to activate once it is subjected to a predetermined pressure and thereafter to control the antenna to emit the signal wherein the control circuitry is configured to control the antenna to produce periodic signals indicative of at least the pressure within the chamber.