This is an achievement/trophy for beating the game without setting off any alarms. This includes everything, from being seen by CCTV cameras, to guards (or civilians) seeing a body that you killed/knocked out. This can happen out of your sight. The Smooth Operator XP bonus is gained when you, specifically, don't get caught. This helps with knowing how well you're doing, but as previously stated, a guard/robot can be alerted, even if he's nowhere near you. Civilians and friendly characters are about the only people that you can allow to see/hear you. The intro level (unaugmented Adam) is included in this..  Tips: 1)Hide ALL bodies. Always. 2)Take out as many guards as possible, so they don't find anything during their patrol. 3)Be thorough while searching levels 4)The acievement is void even if a guard is suspicious. Keep this in mind.
I think #4 suggestion shouldn't be really that strict. What's important is that during all level, no alarms should go loud (unless the alarm is part of the mission, or "scripted"). It HELPS not to be seen, but it's okay to be spotted, as long as the whole level remains quiet. Refer to Foxiest of the hounds for more details. File:Wikia sig.png NicKeL BreaD Talk 14:01, January 15, 2013 (UTC)