Abstract: A bone-conduction loudspeaker set is provided which is similar to the form of a personal ornament. Systems suitable for this are also provided. The bone-conduction loudspeaker set includes: two bone-conduction loudspeaker units; and a loudspeaker-microphone switching unit which switches from a mode where the two bone-conduction loudspeaker units are used as right and left stereo loudspeakers to a mode where one of them is used as a loudspeaker and the other is used as a microphone, and vice versa. A system includes: a mutual-distance detection unit which detects the distance between the two bone-conduction loudspeaker units being within a predetermined distance; and a distress-signal issuance unit which issues a distress signal based on a detection result obtained by the mutual-distance detecting unit.