First things first... Sorry if this gets a bit nerdy, but I have toned down the language as much as possible. Ive just always been really impressed with how complete this game feels, it's so different to most AAA games out there.
So Alien Isolation is one of the best horror games out there, and it only works because the Alien is believably cunning. I think it's one of the most interesting aspects of the game.
If you've ever played Left 4 Dead, you may have heard of its Director AI, where it observed how you are playing and throws different enemies and scenarios at you depending on how well it thinks you are doing. The way the Alien works is kinda similar. It won't act without the Director giving it something to do, and then from there it can work out what to do itself.
You can think of the Director as the Aliens little voice inside its head - it will occasionally point it in the general direction of where you are just to keep the tension up, but it will never specifically point it at you... so the Alien still needs to track you down somehow. So it's possible for you to sneak around it, and it will not find you. However... the Director always knows where the player is, so it's always going to try and keep things interesting.
Like in Left 4 Dead, the Director has a kind of virtual, unseen stress gauge which builds up depending on how close the Alien is to finding you - as it gets more full, and hits a certain point.. the Director tells the Alien to back off to allow the player to relax a bit. This way, the gauge can drip back down, and then the cycle repeats to keep the tension up. The Director doesn't want the Alien to find you every time, but it wants to make you think that it will. It's really something special.
And all of the above is strictly related to the Director, the Alien itself has its own separate AI where it can detect you if you are nearby, or if you touch it, or do something that gives away your location.
If you haven't tried this game, you should definitely try it. Even if you are not really interested in the Alien franchise - it's aesthetically great, the gameplay is good, and did I mention the AI is good too?
There's a great YouTube Documentary on this very topic.. if you're interested.