Couple points I'm gonna hit on.
One, you never told me what to do when I see a student with an object I think looks like a bomb.
Two, you never answered how many false alarms there are. You've said basically X > Y I'd like to know what X and Y are.
Three, I'm gonna wager the number of people who call in bomb threats and then actually have a bomb is very very low. That one time it's real, you don't want people sitting at their desk because you were sure it was just a prank becuase a prank is far far more likely.
Four, I'm slightly concerned by this...
"If you see an unknown device in the hands of a friendly student and think is that a bomb? then you have a major problem."
Who has to be holding an unknown device that looks like a bomb (a critical part) for you to do something? If it was that easy to spot students who would carry out attacks, there wouldn't be attacks. Teachers would spot them in a second.
And I know you go cause I asked you, but how many fire alarms get pulled at your college? If it's anything like the one I work at and the one I go to school at, all the time. You could pull that fire alarm every day for a week and they'll come every time because this time could be a fire.
If you want to argue that people see things as bombs they shouldn't, that's a whole other thread. We can put up pictures and play "bomb or not a bomb". See who's the best.
These are people who aren't trained to deal with bombs, they're trained to deal with children. If I see an item that looks like it could be a bomb, I'm at least getting the principal, and believe me, the principal is no better bomb tech than I am.