Somebody on another thread a few days ago mentioned that the broken window may have set off an alarm if the hotel had that type of system installed. I've tried doing a search to find out, but came up empty.
I have not followed nearly all the articles on this (I will try to get caught up), but I was following it “live” during the hours after the shootings — in one of the earliest articles there was reference to a bellman observing lots of glass crashing down outside the hotel. They might not have known instantly which floor it came from, but they may have known within seconds that a window had been smashed.