Fire alarm in college. Not just the alarm, but also several friends banging on my dorm room door. After the third or fourth try, they assumed I wasn't in and gave up. I woke up eventually because the voices from outside were annoying. (My room was on the third floor at the front of the building and I slept with my window open so everyone gathered outside the front door chatting drifted up...) From that point, my friends asked me to not lock my door...and when I bought a house many years later, I installed fire alarms that also flash lights (because lights wake me up pretty quick).