most smoke alarms work on a small amount of decaying radiactive medium. it emits particles which are picked up my a sensor, this allows the circuit to break and so triggers the alarm. normal smoke from a fire is dense and so the circuit is broken. cigarette smoke isn't that dense but cannabis smoke is more so. its likely at your college they aren't that sensitive. they know that people are gonna smoke and so dont want to have em too sensitive.

when i was at uni my smoke alarm wasn't even a smoke alarm, it was a heat alarm. it didnt go off, even when i made a smoke bomb and set it off in my mates room when he was asleep. it did however go off when i held a lighter underneathe it.

upshot. check if it aint a true smoke alarm you got nothin to worry about. becareful if you disconnect it though cus you mite need it if you are smokeing adn then might check.
you could however replace it with a dead battery. that way it willl never go off.

peace