The watch would first take an initial reading of the vein, and use it to compare to future images. Infrared technology could be employed to capture the images of the veins. If a smartwatch is being used like a key to open a car door or a hotel room, the technology featured in the patent filing could be used to verify one's identity. It also could be used to authenticate a mobile payment, replacing the currently used fingerprint sensor or password sign-in.
The patent, titled "Wearable Device And Method Of Operating The Same," was originally filed in July of last year. If the technology is as impressive as hoped, it could lead to the future use of heart beats as a way to verify identification.
source: USPTO via FastCompany, Phandroid