What if we talk about preventive technology instead? Unfortunately safety is going to mean giving up your personal freedoms when entering a public place - but that is the cost. No idea is too wild - airport style metal detectors on every public door? Personal digital location trackers? Approved, non-lethal stun guns for all? Body scanners as prevalent as street lights? Knockout gas dispensers with fire alarm type pull downs?
I am not sure the right angle, but I do know that I am sick to my stomach.