6 Outstanding DIY Spy Projects
(artigo) DIY hearing implants could allow you to hear through walls
(experimentos simples, sem eletrônica) MAKE A HOMEMADE HEARING AID
Do it Yourself Hearing Aid Repair
<http://makezine.com/2006/08/15/super-ear-super-mic/>
<http://arduinobasics.blogspot.com.br/2013/05/sound-sensor.html>
Electronics project: super hearing aid
diy a hearing aid using a simple 3 transistor circuit