While there are several types and many brands of hearing aids, they all share some common features. Below is an exploded view of a typical Behind The Ear (BTE) and In The Ear (ITE) hearing aid. The parts are as follows:

A) Function Switch - Usually M-T-O (Microphone - Telephone - Off)

B) Battery: Supplies power to the amplifier. Packages are color coded by size: 5a, 10a, 312, 13, 675

C) Microphone: Converts acoustic energy to electrical energy.  Some hearing aids have 2 microphones to improve hearing in noise.

D) T-Coil: Converts magnetic energy to electrical energy. Used for telephone or ALD's.

E) Amplifier or Circuit: Increases the strength of the electrical signal. Also filters and modifies the   response of the hearing aid to match the hearing loss of the user.

F) Volume (Gain) control: Increases or decreases the over-all level of the sound after the amplifier. Many newer hearing aids have automatic gain control.

G) Receiver: Converts electrical energy to acoustic energy.

H) Sound hook (tonal tube): Delivers the sound from receiver to the earmold. May be filtered to further adjust the signal to match the hearing loss.

I) Dispenser's Controls: Fine tuning adjustments made by dispenser or audiologist.