A method of monitoring a subject via an earbud module includes positioning the earbud module within an ear of the subject such that a sensor region thereof matingly engages a region of the ear at the intersection of the anti tragus and acoustic meatus and is oriented in a direction away from the ear canal. Physiological information is then detected and/or measured via the optical sensor. The optical sensor includes an optical emitter and an optical detector, and detecting and/or measuring physiological information about the subject includes directing optical energy at the ear region via the optical emitter and detecting optical energy absorbed, scattered, and/or reflected by the ear region via the optical detector. Environmental information in a vicinity of the subject may be monitored via an environmental sensor associated with the earbud module and subject motion may be monitored via a motion sensor associated with the earbud module.