A page comes in and the silicon-laden recipient has to reach into a pocket, read the number, perhaps punch it into a PDA to find out who is calling and then punch it into a cellular phone. In effect, he or she is devoting considerable mental capabilities to emulating an extremely low-bandwidth communication network. Even low-powered radio waves travel far enough to make eavesdropping and interference a real problem. Since the human body acts like a bag of salt water and shadows radio waves, a device on your lapel might not be able to communicate with one in your back pocket. In addition, the radio spectrum is already crowded, and the licensing requirements for radio communications are complex and vary from country to country.
Infrared communication is limited by line of sight.
Zimmerman understood that security is a serious problem for PANs. Touching a person equipped with a PAN is like tapping a phone line. This is an advantage when an exchange of information is desired, but a problem when privacy is important. Since coming to IBM in 1995, Zimmerman has collaborated with Almaden's Prabhakar Raghavan and Don Coppersmith of the Thomas J. Watson Research Center to develop a security method using encryption that makes the PAN data look like a stream of random bits to would-be eavesdroppers. The version of the PAN that Zimmerman has been showing off is about the size of a pack of cigarettes.