It is a non-invasive test method used in order to determine the reaction of cochlea to auditory stimulants. It is objective, quick, cheap and reliable. Particularly its ease-to-use in newborn screening tests has made auto-acoustic emission (OAE) an indispensable test tool of audiology clinics. Reaction stimulated in inner ear by specific sound stimulants (click, stimulant with two frequencies) sent to inner ear with the help of a probe placed in external auditory canal is recorded by a specifically developed microphone. Furthermore, it has a special mode (Spontaneous Auto-acoustic Emissions) where resting potentials of cochlea are measured without giving any stimulant. Being an objective and reliable test method, OAE can be used easily in many different clinic fields such as patients for whom a hearing test cannot be conducted, very small children, functional hearing loss, retrocochlear pathologies and follow-up of drug auto-toxicity.