All hearing aids have a microphone that picks up sounds and converts them to electrical signals. Those electrical signals go to an amplifier and then to a receiver that converts the signals to sound waves and sends them to the ear. Learn more about the six most common devices. Costs are per aid.

See also: Expert advice on hearing aids.

Mouse over hearing aids to see position on the ear:

Behind the ear (BTE): Plastic tube carries sound to a custom ear mold (not shown). PROS: Larger size makes it easier to manipulate. Tends to last longer than smaller devices. Accommodates directional microphone, volume control. CONS: Conspicuous. Awkward for phone use. COST: $1,200-$2,700.

Mini behind the ear (Mini BTE): Plastic tube connects to an earbud inside the ear canal. PROS: Leaves the ear canal open, for more natural sound, especially your own voice. No custom mold required. No "plugged up" feeling. CONS: Harder to use with the telephone. COST: $1,300-$3,000.

Receiver in canal (RIC): Microphone, amplifier are behind the ear; connected with wires to a receiver in an earbud or custom mold in the canal. PROS: One of the least noticeable devices. Can give superior sound quality. CONS: Harder to use with the phone. COST:  $1,400-$2,900.

In the ear (ITE): Custom-made shell fits in the outer ear. PROS: Easy to insert; can house a directional microphone and volume control; easy to use with the telephone. CONS: Conspicuous and bulky. COST: $1,300-$2,800.

In the canal (ITC): Custom-made device fits into the ear canal opening. PROS: Barely noticeable; large enough for directional microphones and volume control. Cons: Prone to feedback. COST: $1,300-$2,800.

Completely in the canal (CIC): Fits entirely in the ear canal. PROS: Least visible; easy to use with phone; outer ear acts as a funnel, helping with sound location. CONS: Expensive; too small for directional mikes; can be hard to change batteries; prone to feedback. COST: $1,500-$3,700.

– Hearing aids: Morgan Howarth; Ear: Tom Gill/Getty Images

Cathie Gandel is a freelance writer based in the New York City area.

Source: Ann Gentili-Stockwell, audiologist, coauthor of the "Harvard Medical School Special Health Report on Hearing Loss" and director of audiology at Vernick & Gopal, LLC based in Chestnut Hill, Mass. Costs from the Hearing Journal and audiologist estimates.

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