A hearing aid is a device used to amplify a sound and direct it into the users ear. A hearing aid is most commonly used for those with a hearing impairment.http://wordnetweb.princeton.edu/perl/webwn?s=hearing%20aid Approximately 10% of all people have some form of hearing impairment which could benefit from the use of a hearing aid, but far fewer than this wear hearing aids. http://www.hearingaids101.com/

Historically, hearing aids were cone-shaped objects (sometimes called ear trumpets with an uncovered small and large end. The small end could be placed in the ear, with the large end directed at the source of sound, effectively "funneling" the sound waves into the ear for a louder sound. http://wordnetweb.princeton.edu/perl/webwn?o2=&o0=1&o7=&o5=&o1=1&o6=&o4=&o3=&s=ear+trumpet

In more recent times, hearing aids are more often small electronic devices. Worn around the ear, over the ear, or in the ear, modern hearing aids can be very small to maintain concealment. http://www.nidcd.nih.gov/health/hearing/hearingaid.html#hearingaid_04 Using electronics, these hearing aids pick up the sounds in the room and digitally amplify them, directing the sounds to the wearer's ears. These hearing aids can be very simple or very fancy devices, with sound level control and other features. http://www.nidcd.nih.gov/health/hearing/hearingaid.html#hearingaid_01