An earbud includes a speaker driver, and a sensor module secured to the speaker driver that is configured to detect and/or measure physiological information from a subject wearing the earbud. The sensor module includes a printed circuit board, an optical source secured to the printed circuit board, and an optical detector secured to the printed circuit board. A first light guide may be coupled to the optical source that is configured to deliver light from the optical source into an ear region of the subject via a distal end thereof. A second light guide may be coupled to the optical detector that is configured to collect light from the ear region via a distal end thereof and deliver collected light to the optical detector. One or more additional sensors may be secured to the speaker driver, such as accelerometers, humidity sensors, altimeters, and temperature sensors.