• Modern hearing aids are compact enough to custom-fit inside the ear canal.ohr image by Susanne G??ttler from Fotolia.com
  
  Before the invention of the modern hearing aid, people with hearing loss learned to cope by reading lips or having everyone around them shout when speaking. Early versions of the hearing aid were very large and cumbersome. Most were hung on the outside of the ear and attached to a battery pack by a wire. The pack was worn around the neck or clipped to a belt. Today, hearing aids are compact, custom-fitted and virtually undetectable. A hearing aid is an invaluable tool for helping those who cannot hear on their own.
  
  

Microphone

• The microphone on a hearing aid is the part that turns sounds into electrical impulses. When any sound wave contacts the microphone, it is converted into an electrical impulse. A recent innovation to the standard microphone is the directional microphone. This type of microphone is designed to filter sounds coming from behind the wearer by as much as 15 decibels, cutting background noise significantly.
  
  

Amplifier

• The amplifier is a transformer that takes the electrical impulses received by the microphone and amplifies them. Most amplifiers are at least two-stage. The first (pre-) amplifier helps to amplify the input signal with a relatively low gain (the ratio of audio output to input). The signal is further amplified by the second (power) amplifier. Classified by type, these amplifiers are identified by power consumption, output and gain.
  
  

Receiver

• The receiver takes the amplified electrical impulses and converts them back into sounds. This part of a hearing aid fits in the external ear canal and is most often the part that is seen. With innovations in technology, the receivers are now quite small. Unfortunately, small receivers do not have the output that larger ones do and can become clogged with debris from the ear or damaged when dropped.
  
  

Battery

• Hearing aid batteries are small, button-type batteries that come in various sizes depending on the type of hearing aid in use. The most common types of batteries are called zinc-air batteries and are activated by removing the paper tab from the battery's back. This allows air to interact with the zinc in the battery. Most hearing-aid batteries will last five to seven days under constant use.