Technofile : Can't kill, won't kill

An automatic pistol that shoots only in the hands of police officers is being
developed by Colt’s Manufacturing Company. The “smart” gun fires on a signal
from a transponder that sends out radio waves carrying a unique digital code.
The transponder is so small it can be hidden in a ring, watch or shirtsleeve
button and has a range of about 20 centimetres.