Armed teachers or security guards? Oh, wait; the majority of teacher types have been inculcated with the irrational liberal fear of firearms.
Federal law actually forbids the possession of any firearm on any school property, private or public, even by a police officer responding to a school shooting. That absolutely prohibits armed teachers or security guards. School officials also cannot cause any physical harm to any student, even if armed, dangerous, and on a rampage.
School rules prohibiting wireless communication devices, however, do not apply to security guards, administrators, educrats, and certain authorized teachers with specialized security training. Anyone else found in possession of any such device automatically is considered a drug dealer and punished as such. Or so it was when I was in school. With cellular-telephone mania nowadays, things might have changed in the past decade.