> If such tech was required by law, any criminal with a jammer would create a zone where only they could shoot.

I don't see why the system would do that. A "fail-safe" doesn't always mean failing closed; sometimes it means failing open. That is, if there is a jammer, then fall back to letting anyone shoot anyone, which is no worse than things are now. If there isn't a jammer, then let the law say who can shoot people.

(Yes, then anyone can buy their own personal jammer to make their gun "work." People can also override those breathalyzer-meters that they have to blow into to get their cars to start. But, by-and-large, do they?)