Biometrics–the technique of using something unique about your body as a security device–promises to improve safety while being more convenient than a password. Fingerprints, retinal scans, and voice identification have all found some use, although not without limitations.
Now researchers in Germany want you to use your head, literally. SkullConduct measures vibrations of your skull in response to a sonic signal. A small prototype was successful and is particularly well suited for something you are holding up to your head anyway, like a smartphone or a headset like a Google Glass.
There are some limitations, though. For one thing, background noise can be a factor. It stands to reason, also, that more testing is necessary.