Intrabody Signalling

In 1995 Tom Zimmerman and Neil Gershenfeld realized that the weak low-frequency fields that the Physics and Media Group were using for sensing contained information that was being used to separate them from background noise. Instead of otherwise ignoring this information, it could be modulated to send data through the body to create a Personal Area Network (PAN). This means that personal information stays with the user where it belongs rather than being radiated out to the surroundings where it could cause interference or be eavesdropped, and that physical gestures can contain logical meaning so that a handshake could exchange business cards, a hand on a doorknob could unlock it, or fingers touching a keyboard could transmit a cryptographic key.

Here is a link to a paper explaining how it works.

This MPEG clip (16MB) shows the PAN system in action.

This photograph (linked to a larger version) shows a shoe made by Rehmi Post containing a PAN transmitter (pulled out for clarity), and in the foreground is Matthew Reynold's PAN III RS232-to-body modem.