This paper introduces a peripheral device that supports communication especially in terms of expressive power in mobile environments. As people can speak and hear while doing something else without losing concentration very much, sound has been chosen as a communicating medium not to prevent the daily use of the device. Referring to the conditions recognized by an electronic sensory system, the device modifies both incoming and outgoing communicating sound from and to somebody else and the user’s self. An implementation of headset computer with variety of sensors and experimental results are also described in this paper.