Only hearing optimally out of one ear can be very disorienting. So for the best experience and the highest quality of life, all Sontro OTC Hearing Aids are sold as a set because the brain processes hearing signals from both ears for improved clarity and a more balanced sound.Even though you may only have hearing loss in one ear, both Sontro OTC Hearing Aids will need to be programmed at the same time to optimize your hearing assessment.  After programming your Sontro OTC Hearing Aids to the OtoTune app, you can then use only the one hearing aid to amplify sound in the ear with hearing impairment.