Abstract: A hearing aid module includes an elongated housing, an optical sensor module within the housing, an audio driver positioned within the housing adjacent the optical sensor module, and first and second light guides positioned near the audio driver. The module has a rectangular configuration with opposite first and second sides, opposite third and fourth sides, and opposite first and second ends. The first and second sides each include an opening. An ear tip is coupled to the housing first end and is configured to retain the module within the auditory canal. The first light guide guides light from an optical emitter through the opening in the housing first side and into skin of the auditory canal in a non-line of sight manner. The second light guide collects light from the skin of the auditory canal and directs the collected light to an optical detector in a non-line of sight manner.