Researchers at the University of Buffalo created a new authentication tool called EarEcho. The team modified a set of off the shelf earbuds with a tiny microphone that points inside the wearers ear, not out towards the world around them. The tiny mic is tuned to listen to the echo of sounds as theyre played and then propagate through the ear canal. It was able to authenticate the wearer around 95 percent of the time given just one second of ear canal recording, and 97.5 percent when the recording was increased to three seconds.”]
Source: https://gizmodo.com/researchers-think-its-a-good-idea-to-secure-your-phone-1838248232