I know they did the whole of westwood on a saturday morning last year - starting from about 5:30 - 6am i think. Someone in my house last year (Derhill 3) said that he woke up at about 6:30 and could hear the alarms getting closer.
Also, if the fire alarm goes off and you are in the shower, dont get back in the shower as soon as you get back in the building. Last year someone had to get out of the shower cause someone set an alarm off in the kitchen, so he was standing outside covered with not much more than a towel, soaking wet. About 3 mins after we were let back in the alarm went off again...just giving enough time for my housemate to get back into the shower again.