Amazon patents technology to unlock your phone using the shape of your ear. See more information about this idea and related technological aspects in the following video:
According to the patent description:
An electronic device can attempt to capture at least one image including at least a portion of a user’s ear when the user utilizes the electronic device for certain purposes, such as to receive a call or listen to an audio file. In some embodiments, the device analyzes the captured information to determine whether the user is holding the device near the user’s right ear or left ear, and adjusts functionality of the device based at least in part upon how the user is likely holding the phone. In other embodiments, the device attempts to recognize the user based on ear shape or other parameters, and can provide customized functionality of the device based at least upon that determination.
Link to the patent description: USPTO