An assembly of at least one radiation detector, at least one radiation emitter and a housing configured to be positioned inside the ear canal of a person or animal, the detector(s) and emitter(s) being provided in or on the housing, the emitter(s) being configured to emit radiation away from the housing and the detector(s) being configured to receive radiation directed toward the housing. No overlap may be provided between the field of view of the radiation detector(s) and the emitter(s), such as by providing a blocking element.
