I have very useful idea about security in public places and prevention such terroristic acts as shooting in schools and other places, without restrictions of free guns trading in U.S.
U.S. government can ask guns manufacturers to implement GPS tracking chip into any gun, which they produce, to allow U.S. police see any movements near schools and other public objects on GPS monitor if a gun owner getting closer, for example, less than 100 feets and prevent tragedy before it's happen. To avoid any doubts about personal privacy of people who have a gun - this chip may be set to send a signal only if an owner is closer to an object than allowed distance. Chip can be charged by well known technology, which allows to charge devices from vibrations.