Abstract: A listening device for detecting audio frequency sounds and presenting them at increased sound levels to a user's ears. The listening device comprises a lighweight housing with a sound port disposed on a front wall and containing audio processing components for detecting input sound waves, amplifying them, and transferring them to bi-aural sound transfer means coupled to the housing. The bi-aural transfer means directs amplified sound to both ears of a device user simultaneously. The listening device is very lightweight and very compact, with the main housing being less than about 1 cubic inch in volumeThe listening device employs an acoustical connector on the front wall to allow efficient transfer of sound waves from a series of acoustical adapters, generators, and probes. One such probe is highly useful for automotive engine analysis and another is highly useful for medical applications.