A performance monitoring system includes an athletic band or other article of apparel worn by a user, with a pocket supported by the article and defining a cavity, where the pocket has a sensor opening extending through an inner wall of the pocket and an access opening providing access to the cavity. The system also includes an electronic module received in the cavity such that the module can be inserted and removed from the cavity through the access opening. The module has a projection on an underside of the electronic module and a sensor mounted on the projection, where the projection extends through the sensor opening when the electronic module is received in the cavity and is configured to place the sensor in close proximity to skin of the user, such that the sensor is configured to sense a physiological parameter of the user.