"A portable, battery-powered device worn around the neck intended to receive sound from an audio source [e.g., mobile (cellular) telephone] wirelessly (e.g., via Bluetooth) and transfer it via an audio frequency magnetic field to a hearing aid with an induction coil (i.e., bypassing the hearing aids microphone) when it is switched to the ""T"" or `?MT?? position, in order for the hearing aid user to hear (e.g., telephone conversation, music) more clearly. It typically consists of small active amplifier with a wire loop worn around the neck. It may also include a microphone for hands-free telephone conversation."