Japanese scientists have invented a way to store up to 5 megabits of data onto a human fingernail using femtosecond laser pulses. The data lasts for approximately 6 months, which is the length of time it takes for the body to completely replace the fingernail tissue. Researcher Yoshio Hayasaki notes:

I don't like carrying around a large number of cards, money and papers... I think that a key application will be personal authentication. Data stored in a fingernail can be used with biometrics, such as fingerprint authentication and intravenous authentication of the finger.

(Via Mahalanobis.)