There are total of three big Rooms, two little Rooms, a Floor and a Tunnel to clear. In the big three Rooms you have Alarmtriggers that be actived by the Enemies to call reinforcements. In the first big Room is one Trigger, in the second big Room is one again and in the last big Room are two Triggers. The Enemies trigger the Alarms automatically but make sure you hear the Alarm when you fight in this three Rooms!. Before you go to the next Area make sure you have kill all Enemies. Look in every dark Corner, behind every Crate etc. Sometimes a Enemie spawns when you kill all others in this Area.