Start a timer at 6
every action roll decreases the timer by 1 (exceptions if multiple action rolls happen at the same time i.e if 2 players are searching different rooms)
If the players are ever spotted the timer drops by another 1
If Loud combat occurs or an NPC has the time to call for help then the countdown reaches zero and then resets. This only occurs if the Timer has not reached zero once. if it has then the countdown drops by 2

If the countdown reaches zero the first time then all adversaries in the scene have the feeling that something is wrong and begin to investigate
if the countdown reaches zero for the second time then a commander shows up and Fear can be used to add minions and standard adversaries to the scene
if the countdown reaches zero for the third time then a Tier 2 commander shows up and Fear can be used to add Tier 2 minions to the scene.

If the players go loud then the countdown reaches zero for the first time and changes to a 4. It then decreases each time the player's roll with Fear or if the GM spends Fear to decrease it.

If the area has a lot of camera's then all checks to move stealthily are at disadvantage

As long as the players haven't gone loud then any Tier 1 target can be knocked out with a successful attack, damage does not need to be rolled.