We all know that there are certain physical characteristics that are totally unique to each individual. Your fingerprints, for example, are entirely unique—no one else has fingerprints exactly like yours. The pattern of your iris, the colored part of your eye, is totally unique. So is your DNA. But did you know that your heartbeat is completely unique too? Every person on earth has a different heartbeat pattern, or “cardiac signature.” Your cardiac signature cannot be altered or disguised. So, if someone can measure your “cardiac signature,” they can identify you, even in a big crowd of people.

In fact—and this is pretty scary to me—the Pentagon has built a laser that can identify people by their heartbeat from 600 feet away. There are positive uses for this technology, of course. Doctors…