What stealth elements are there in BioShock 2?
Solution 1:
From what I known from playing Bioshock 2 as stealthy as possible:
- You will get sneak bonus if you manage to kill the enemy unalarmed (which are unseen, quietly, no bell alert ringing etc)
- Enemy will react to sound, especially gunshots and bell alert. But before they can hunt you down, they must seek you first
- Different surface will produce different level of sound, so stealth while on a pool of water = not good
- Crouching and darkness/shadows will improve stealth.
- You can indeed sneak up enemies from their back, as long as they don't turn their head around
- Hiding from a different floor level works (exp. you on the 2nd floor, bad guys below the stairs) but watch out for noises (walking, grinning with your drill etc)
- Alerted enemy will hunt you down for a period of time before they continue their routine. They will also alert each other and will search for your at the last spot they thought you were
- Stealth killing enemy near another enemy WILL alert them although they don't see you (because of the noise)
I don't know about changing game difficulty will or will not affect detection BUT anything I told you doesn't really matter TBH because once you're spotted, gunning them down is way easier than run and hide. Honestly this game is a shooting game and stealth is not a way to enjoy it.
Solution 2:
In addition to (and contrary to some points of) this other answer, and from my experience:
Enemies will only react to weapon sounds if you are near them. I have used the spear gun from a far location and occasionally missed enemies by a few inches and hit wall or objects near the enemy. They never noticed that they're being shot at (probably because of the distance).
Surface is not a factor in sneaking. The speed of your walking is more of a factor (you are less likely to be noticed if you're walking slowly or crouch-walking).
Shadows or light levels do not seem to be a factor at all.