There are many types of hearing aids (also known as hearing instruments), which vary in size, power and circuitry. Among the different sizes and models are:
Behind the ear aids (BTE): BTE aids consist of a case, a tube and an earmold. The case is small and made of plastic. Generally, the case sits behind the pinna (ear) with the tube coming down the front into the earmold. The case contains the amplification system. The sound is routed from the hearing aid case to the earmold via the tube. BTEs can be used for mild to profound hearing loss. Due to the electrical components being located outside the ear, the chance of moisture and earwax damaging the components is reduced.
In the ear aids (ITE): These devices fit in the outer ear bowl (called the concha); . ITE hearing aids are custom made to fit each individual’s ear. They can be used in mild to some severe hearing losses.
Receiver In the Canal/Ear (RIC/RITE): With a RITE hearing aid, the speaker is right in the ear canal and the amplified output of the hearing aid does not need to be pushed through an acoustic tube to get there, and is therefore free of this distortion. Secondly, RITE hearing aids can typically be made with a very small part behind-the-ear and the wire connecting the hearing aid and the speaker is extremely inconspicuous. For the majority of people this is one of the most cosmetically acceptable hearing device types.
In the canal (ITC), mini canal (MIC) and completely in the canal aids (CIC): ITC aids are smaller, filling only the bottom half of the external ear. You usually cannot see very much of this hearing aid when you are face to face with someone. MIC and CIC aids are often not visible unless you look directly into the wearer’s ear.  These aids are intended for mild to -severe losses.
Invisible In canal hearing aids (IIC): This type of hearing aid fitting is not visible when worn. This is because it fits deeper in the canal than other types, so that it is out of view even when looking directly in to the ear bowl (concha). A comfortable fit is achieved because the shell of the aid is custom-made to an individual ear canal after taking a mould of the patient’s ear.
Open-fit devices: “Open-fit” or “Over-the-Ear” OTE hearing aids are small behind-the-ear type devices. This type is characterized by a small plastic case behind the ear, and a very fine clear tube running into the ear canal. Inside the ear canal, a small soft silicone dome or a molded, highly vented acrylic tip holds the tube in place. This design is intended to reduce the occlusion effect.
Bone Anchored Hearing Aids (BAHA): The BAHA is an auditory prosthetic which can be surgically implanted. The BAHA uses the skull as a pathway for sound to travel to the inner ear. For people with conductive hearing loss, the BAHA bypasses the external auditory canal and middle ear, stimulating the functioning cochlea. For people with unilateral hearing loss, the BAHA uses the skull to conduct the sound from the deaf side to the side with the functioning cochlea. Individuals under the age of 5 typically wear the BAHA device on a headband. Over age 5, a titanium “post” can be surgically embedded into the skull with a small abutment exposed outside the skin. The BAHA sound processor sits on this abutment and transmits sound vibrations to the external abutment of the titanium implant. The implant vibrates the skull and inner ear, which stimulate the nerve fibers of the inner ear, allowing hearing.