I'm about half way through my second playthrough of the game now, and realised that on the first mission at Milwaukee Junction a turret did see me. My minimap went to "hostile", but the turret did not fire, and (as far as I can tell) no alarm sounded. Being seen by any turret appears to immediately turn the minimap to saying "hostile" — there is no 'alarmed' phase for turrets, it appears.
Does this disqualify me from Foxiest of the Hounds?
Best Answer
Areas with alarms have those red lights dotted all over the map. When those start to flash, it means the alarm has been triggered. This is how I usually tell, as sometimes I might accidentally set off the alarm without even knowing.
Just to answer your question, under normal circumstances, as mordi2k has mentioned, as long as a turret doesn't start shooting at you, then you are safe. However, in this case there is actually no Smooth Operator bonus for the first mission in the Sarif Manufacturing Plant, hence no danger of breaking the Foxiest of all Hounds achievement to start with.
You might want to read the answer I posted on this thread:
Which missions can I earn the Ghost and/or Smooth Operator bonus on?