In the mobile world, there are arguments over the accuracy and security of biometrics such as fingerprints, irises, and faces. In the security and military sectors, however, people are turning to heartbeats. Just like fingerprints, the cardiac signature of a person is believed to be unique and infallible. But unlike fingerprints, heartbeats can be measured secretly from a distance with a laser. And wouldn’t you know it, the US military has one exactly like that.