Things like ShotSpotter are only fighting the symptoms. As an european I find it ridiculus to hear that such thing even exists. Why would we not simply ban the guns themselves?
The US shares a 3,145 kilometer long border with Mexico, unfortunately there are at best 1,044 km of border 'barriers' in place. People, guns, money and drugs are smuggled across the border daily.
In the context of banning guns, any movement north is too much.
I have nothing in principle against a society that completely bans guns, but are you prepared to strike enough terror into the population that breaking the law and getting guns anyway becomes unthinkable?