While there is definitely an application for this in the right market (Guns carried by people who are likely to have their weapons turned against them) but it's hardly a sollution to so-called "Gun violence". Just like the so-called "Assault weapons ban" which banned things like high-capacity magazines and so forth, is that preban hardware was legal. Furthermore, given the extreme variety of arms in public circulation, retrofitting them all would be impossible. And then there is the issue of antique arms that cannot be retrofitted for historical reasons yet still remain very effective weapons.