Former DARPA Director and now Google Executive, Regina Dugan: ID Microchips.

She goes on to explain how the microchip works once inside the body. The pill has a small chip inside of it with a switch, when you swallow it, the acids in your stomach serve as the electrolyte and that powers it up. And the switch goes on and off and creates an 18 bit ECG wide signal in your body and essentially your entire body becomes your authentication token.

Just FYI this video is from 2012, so you can imagine the tech they already have.