The Armatix smart gun is implanted with an electronic chip that allows it to be fired only if the shooter is wearing a watch that communicates with it through a radio signal. It is not sold in the U.S. Michael Dalder/Reuters/Landov hide caption

itoggle caption Michael Dalder/Reuters/Landov

Flags fly at half-staff Tuesday after the deadly shootings at the Navy Yard in Washington, D.C. J. Scott Applewhite/AP hide caption

itoggle caption J. Scott Applewhite/AP