Introduction

Guards and professionals won't see you if you are directly above them hanging onto the ceiling.



Walls above doors (as shown below) are excellent hiding spots as enemies has fields of vision vertically only up to 45 degrees upwards. If you have two doors in short distances of each other (like the image on the right) you can hide there indefinitely.





Guards and professionals won't see you if you are inside the elevator. (As the game hint says)



Guards (not professionals) have reduced vision if the room is dark. However, if you are in a lit zone (Outside or a lit room) they can see you at the normal distances of which they see things.



Elevators will switch the facing of the guards and professionals when arriving that floor



Guards and professionals has a slight delay to look for the light switch if they are standing when the lights goes off. in the setting below, If you turn off the light, run left and use the camera to close the door, even the professional can see in the dark he will not see you when he turns around.





One use of Hushcracker will silence all the layers of glass you are breaking until you touch solid wall/ground/ceiling. Each piece of glass costs you 1 battery so breaking 3 at a time will cost you 3 batteries all at once.



Guards already on patrol do not actively try to use hand scanners to open doors even if the door closes right in front of them. However they will use the handprint scanner if the lights turn off while they are patrolling.

Edit3: Final stage updated for the impossibility of Perfect Gentleman if you choose Rooke: The Killer before.

The guides I found around this achievement usually involves kicking down doors, which you can only do once you unlock the final stage. This guide center arounds the ability of unlocking the achievement as you progress in the game.I have skipped the stages without guards (Rooke: Caught on Camera, Rooke: Crossed Wires, Collins: innocent, you need guards to get the achievement) because they fall outside the purpose of this guide. The stages where you need Gatecrashers for the achievement is in the Addendum (Rooke: Mains and the final stage). There are less reproducible ways to complete Rooke: Guarded and Rooke: Mains with Perfect Gentleman, so it will take numerous save/load and your mileage will vary.Skills/Concepts you'll need:tl;dr: The list of video playthroughs can be found here Please rate the guide if you find it useful.Edit: Gessler: Acquisitions is added to the list of stages.Edit2: Rooke: The Plant and Jackson: the Truth/ Rooke: The Killer is added. This accounts for all the stages Starting from Rooke: Three for All all the way to The 2nd last stage.Edit4: Rooke: Guarded and Rooke: Mains is up, although not very reproducible at this stage.Edit5: Final stage fixed to include Hightower. This covers all stages with guards, although a couple of them is rather not reproducible at this point.