How to send a password through your body

Using their method, a person just needs to be touching a transmitter—the fingerprint reader on an iPhone, for example—when he or she comes in contact with a receiver. In the doorknob example, the metal handle is hooked up to a reader that listens for electromagnetic pulses. A code sent from the iPhone’s fingerprint reader travels across a layer of particularly conductive tissue right beneath the outer layer of human skin. It quickly propagates to every part of the body, so that your entire epidermis glows, invisibly, with data. (The researchers were able to detect signals sent from one arm to the opposite leg, and could accurately read them whether the person was standing, sitting, or lying down.) When the signal arrives at the doorknob, the reader makes sure it’s the right passcode and, if it is, it opens.

This same approach could also be used to securely pair wearable devices—everything from calorie counters to insulin pumps—with their owners and each other. The technique takes advantage of the fact that most devices give off faint electromagnetic signals when they’re used normally. Some gadgets, like fingerprint readers and trackpads, produce particularly reliable signals, said Vikram Iyer, one of the two lead authors on the paper that presented the findings.