AoO against an unknown threat?

[Alzrius]

I can't seem to find this in the SRD, though I'm sure it has to be there somewhere, but are there rules regarding the availability of an AoO if you're unaware of the creature provoking it?

A good example is if an invisible creature is moving through your threatened space. Similarly, what if you're blinded (or just in the area of a deeper darkness spell) and a target moves through your threatened area? Do you still gain an attack of opportunity in those instances?

 

[Kask]

I can't seem to find this in the SRD, though I'm sure it has to be there somewhere, but are there rules regarding the availability of an AoO if you're unaware of the creature provoking it?

It is called attack of opportunity. If you don't know about it, you don't have an opportunity.

 

[irdeggman]

The examples you are asking about are already covvered (you can't make an AoO).

Total Concealment: If you have line of effect to a target but not line of sight he is considered to have total concealment from you. You can’t attack an opponent that has total concealment, though you can attack into a square that you think he occupies. A successful attack into a square occupied by an enemy with total concealment has a 50% miss chance (instead of the normal 20% miss chance for an opponent with concealment).
You can’t execute an attack of opportunity against an opponent with total concealment, even if you know what square or squares the opponent occupies.

Blinded: The character cannot see. He takes a –2 penalty to Armor Class, loses his Dexterity bonus to AC (if any), moves at half speed, and takes a –4 penalty on Search checks and on most Strength- and Dexterity-based skill checks. All checks and activities that rely on vision (such as reading and Spot checks) automatically fail. All opponents are considered to have total concealment (50% miss chance) to the blinded character. Characters who remain blinded for a long time grow accustomed to these drawbacks and can overcome some of them.

INVISIBILITY
The ability to move about unseen is not foolproof. While they can’t be seen, invisible creatures can be heard, smelled, or felt.
Invisibility makes a creature undetectable by vision, including darkvision.
Invisibility does not, by itself, make a creature immune to critical hits, but it does make the creature immune to extra damage from being a ranger’s favored enemy and from sneak attacks.
A creature can generally notice the presence of an active invisible creature within 30 feet with a DC 20 Spot check. The observer gains a hunch that “something’s there” but can’t see it or target it accurately with an attack. A creature who is holding still is very hard to notice (DC 30). An inanimate object, an unliving creature holding still, or a completely immobile creature is even harder to spot (DC 40). It’s practically impossible (+20 DC) to pinpoint an invisible creature’s location with a Spot check, and even if a character succeeds on such a check, the invisible creature still benefits from total concealment (50% miss chance).