A device that amplifies sound and directs it into the ear canal. A hearing aid usually consists of a microphone, amplifier and receiver. Hearing aids come in 4 basic styles: In the Ear (ITE), behind the ear (BTE), body aid and eyeglass hearing aid. Body aids are seldom used except for profound losses. Eyeglass hearing aids had their heyday in the 1960s and 1970s. They are not used today.