I've triggered an alarm, what does that mean?
Alarms seem to cause any nearby mobs to come to your location, but they do that most of the time anyway so it's not necessarily a big deal if you're well prepared.
When playing recently, an alarm set off a few rooms away from a room I had earlier seen a particular enemy seemed to cause it to head towards my position, causing it to meet me in the corridor on the way back.
So I'm fairly sure that is the intended effect of the alarm, but I don't know if the alarm ranges the entire level, nor it's duration.