A light-guiding earpiece configured to be worn by a subject includes a base comprising a speaker and at least one optical detector, a housing extending outwardly from the base that is configured to be positioned within an ear of a subject, and a flexible optical emitter configured to be conformable to at least a portion of the earpiece. The housing encloses the speaker and comprises at least one aperture through which sound from the speaker can pass. The flexible optical emitter may be integrally formed within the housing, and the housing may include translucent material that forms a light-guiding region through which light from the flexible optical emitter can pass. The optical detector may be a flexible optical detector.