Okay, given that the Hadley's aliens could've gotten to Newt at any point, hypothetically, why didn't they? Was it just dumb luck that she managed to be the last one alive?
I'm going to stick to Cameron's original intention that Newt was able to fit places even the other children couldn't go. Given I don't really feel like getting into a drawn out debate on the layout of a fictional space colony, I'll choose to believe that Newt was able to squeeze into little spaces where the warriors couldn't reach or fit, and short of suiciding themselves to melt.. something above her or jack-hammering the entire section of wall/floor/whatever, they simply left her alone or were too busy getting the rest of the colonists, which were in a far easier location to breach.
This also brings up the Aliens ability to solve problems. Getting into a barricaded building would be a lot easier than reaching a little kid that's stuffed themselves into some nook at the ass end of some vent somewhere, scared out of their minds. A door is an obvious point of travel, so the Aliens bashed it down. The use of acid to gain entry is also implied in Aliens, though we don't see them do this directly. However, this is still basic problem solving. I mean we don't see them ramming their heads through the walls to get somewhere even though they might, eventually, be able to.
Realistically it could be any of these answers. They were too preoccupied, Newt just got lucky, or she actually managed to physically evade them for a time (though obviously this wouldn't work forever due to the need for food.)
Back to the OP, I would prefer it if the player wasn't ever sure how the Alien could sense, so they had to limit all factors and just hope for the best. Light, sound, etc.. There's plenty of evidence that the Alien can hear, at least from the first film.