Underskin is a concept for a smart digital tattoo which would be implanted in your hand and interact with everything you touch, including unlocking doors, trading data with a handshake, paying when you don’t have your credit card at hand, or even tell you if you have low blood sugar. Because it runs off body’s electro-chemical energy, Underskin does not need batteries and would always be on. The device would also monitor your vitality with precision.