That's my whole point. Maybe you guys went to super cool schools with no crime.
I went to schools that had periodic bomb threats requiring full school evacs, fights, massive petty theft, and the usual assortment of messed up kids that were waiting to go off, plus an administration that generally didn't care if you were bullied. Plus there were also the usual assortment of kids that had to report to parole officers. Crime free? Hardly.
And you were the only one who didn't go "Oh my god, metal detectors?! Security guards?!?!" So you probably know just how bad some schools can get, examples obviously above.
But on to the real question about teachers in your school. So they
shouldn't go get someone to check out a device because why again? One would think a school with that amount of issues would be one to have teachers on a stronger lookout for bomb like things.
I doubt your teachers were trained police officers, what did they do in events that needed cops? What do you think teachers do in terms of fights, attacks, drug deals, etc etc? You get the administration and if they can't handle it, they call the cops. Just because bomb is the rarest of the rare doesn't mean you stop doing it.