A performance monitoring apparatus comprising an assembly of a performance monitoring module and a general purpose portable telecommunications device such as a mobile telephone or mobile smart phone connected for data communication mounted on a common casing. The performance monitoring module is adapted for receiving performance signals from at least one performance sensor and for converting the performance signals into performance data. The general purpose portable telecommunications device is configured to be activate-able to cause the performance monitoring module to transfer performance data to the general purpose portable telecommunications device. The common casing comprises mounting means for mounting onto a support surface. This module is adapted for cooperative operation with a general purpose portable telecommunications device to expand its processing and display power while maintaining a low cost simple design and compactness.