What are the criteria to gain the stealth bonus experience at the end of missions?

What are the rewards you can receive at the end of missions for a stealth approach and how does it compare versus killing every enemy you come across in terms of experience and rewards.

Can I do take downs on enemies I come across and still receive the Ghost bonus? Since technically no one has seen me.

Also, do turrets count as being detected by a hostile?

This post is a wiki post. Please feel free to edit it, but with first-hand information only.

First-hand testing has established that the Ghost rating is still achievable with:

• A camera becoming "suspicious",
• Turrets seeing you, firing at you and getting destroyed by you, as long as no living enemy seen/heard it,
• A guard getting "alarmed" by seeing/hearing an effect, like a very short (<1 sec) visual PC presence, a door opening, jumping or gunshot,
• Killing or knocking-out enemies with a takedown from behind, if nobody saw you,
• Insta-killing someone (probably with a headshot), as long as they didn't have a chance to see you & react, and nobody seen it,
• Insta-knocking out an enemy with a tranquilizer dart to the head (you'll see the Marksman reward), if nobody sees it - note that not every enemy (particularily those with heavy helmets) can be insta-knocked out.

However, you will not get the rating if:

• Enemy sees player for a bit longer (getting Hostile in the meantime), touches player or sees him carrying something,
• Any enemy sees a bot/turret destruction, ally death or an unconscious/dead body,
• Enemy sees a gunshot (only hearing it is still OK!).

Note that having a "Hostile" enemy doesn't automatically mean you lost "Ghost"; e.g. a lone enemy attacked by reprogrammed turret would get Hostile, but you still can get Ghost in that situation, if all the other conditions are met.

For more reference & test cases, see http://deusex.wikia.com/wiki/Ghost_%28bonus%29

Note that the Smooth Operator reward is an "easier" version of Ghost, which only applies to avoiding triggering installed alarm-systems, not detection or combat with guards themselves. (It cannot be rewarded for passing areas that lack such systems.) Smooth Operator is used for the Foxiest of the Hounds achievement.

Takedowns will not prevent you from receiving the Ghost bonus. I haven't verified it for sure, but being spotted by a turret almost certainly will.

The best way to tell if you're still eligible for Ghost after a close call is to check your mini-map. Any time enemies enter the "Hostile" state, as indicated by the label above the map, you've been spotted and you will not receive the bonus. The "Alarmed" state is when enemies think they've seen or heard something but aren't sure what it is, so causing an enemy to enter that state will not prevent you from getting the bonus.

I'm not sure about Smooth Operator. I've seen conflicting information about it: some people say you get it as long as you don't trigger an actual audible alarm, whereas others say you must not put enemies into the "Alarmed" state.

I managed to get the ghost stealth bonus while using both knockout and take-down kills on enemies. I managed to not cause any alerts and avoided detection from all turrets, so I'm still not sure if turrets count as being detected.

So the ghost stealth bonus and getting xp/loot from knockouts and kills are not mutually exclusive.

I did NOT get smooth operator, however, or I just missed that popup notification or something else happened. But I positive I did not cause any alert states or trigger any alarms. Its possible my takedowns caused me to miss out on that bonus.