On the Displace level where you can kill two men, one resets all alarms, but the other man sets them back to whatever number they were. The first is in the room with the computer and books on the desk. It is near the boiler room. Knock him out first and shoot him with the 5-7 pistol. The next man is in the room after you get out of the vent shaft. You can kill any enemy on a no killing mission if you do it this way. The third person that does something on this level is the one guarding Milan's office. He leaves blood stains resembling a gun. Note: These only work if you wear the National Guard costume, found on the ledge in Manhattan. The ones featuring alarms (the first and second men) only work on a random basis.