A belt drive monitoring system comprising: a driver pulley; a driven pulley; the driver pulley and driven pulley connected by an endless member a first magnetic member having a magnetic field attached to the driver pulley a second magnetic member having a magnetic field attached to the driven pulley; a first sensor disposed to detect a changing magnetic field caused by passage of the first magnetic member; a second sensor disposed to detect a changing magnetic field caused by passage of the second magnetic member; a first transmitter configured to wirelessly transmit to a receiver a first data signal from the first sensor and a second transmitter configured to wirelessly transmit to the receiver a second data signal from the second sensor; and the receiver configured to manipulate the first data signal and the second data signal whereby a system parameter is calculated and provided to a user; characterised in that: the first magnetic member comprises a first plurality of magnets that are arranged about a perimeter of the driver pulley at a first radius from an axis of rotation of the driver pulley with a predetermined first spacing between each adjacent magnet; and the second magnetic member comprises a second plurality of magnets that are arranged about a perimeter of the driven pulley at a second radius from an axis of rotation of the driven pulley with a predetermined second spacing between each adjacent magnet. a driver pulley; a driven pulley; the driver pulley and driven pulley connected by an endless member a first magnetic member having a magnetic field attached to the driver pulley a second magnetic member having a magnetic field attached to the driven pulley; a first sensor disposed to detect a changing magnetic field caused by passage of the first magnetic member; a second sensor disposed to detect a changing magnetic field caused by passage of the second magnetic member; a first transmitter configured to wirelessly transmit to a receiver a first data signal from the first sensor and a second transmitter configured to wirelessly transmit to the receiver a second data signal from the second sensor; and the receiver configured to manipulate the first data signal and the second data signal whereby a system parameter is calculated and provided to a user; characterised in that: the first magnetic member comprises a first plurality of magnets that are arranged about a perimeter of the driver pulley at a first radius from an axis of rotation of the driver pulley with a predetermined first spacing between each adjacent magnet; and the second magnetic member comprises a second plurality of magnets that are arranged about a perimeter of the driven pulley at a second radius from an axis of rotation of the driven pulley with a predetermined second spacing between each adjacent magnet. the first magnetic member comprises a first plurality of magnets that are arranged about a perimeter of the driver pulley at a first radius from an axis of rotation of the driver pulley with a predetermined first spacing between each adjacent magnet; and the second magnetic member comprises a second plurality of magnets that are arranged about a perimeter of the driven pulley at a second radius from an axis of rotation of the driven pulley with a predetermined second spacing between each adjacent magnet.