The proliferation of street thuggery and the modern ' * hero' movies work hand in hand to normalise this behavior - actions on screen that would harm/kill in real life are thus entering the daily social interactions in the teen/preteen milieu = guns/knives widely carried. In my youth all weapons in street conflicts were not employed = a form of self limiting interaction.
Now knives/sticks/guns are commonly carried.
Millimeter radar can easily detect metallic objects of small size, and if allowed, might easily alert police to them. They will not detect fiberglass knives, as a few prison systems found when they found a number of undetectable shivs made in the prison shop this way. These knives were not good for whittling, but were good as a prison shiv. Knowledge of this is widespread in prisons and a there are a wide array of contraband items not allowed in visitors hands. This list grows daily.
I was a prison volunteer a few years ago, and was involved in counselling inmates, escorting them on public visits etc. There is a violence/weapon based pecking order in prisons and those with zero weapons=most pecked. Of course, we tell them most pecked = first out, as those caught with/using weapons = last out.
We had photo/video of all this stuff to educate the volunteers/guards what to look for. So when I see a super hero movie, it makes me think of life in a prison on screen...