Im not inferring that it has such technology, but Bishop asked the Sulaco computer whether there was an alien onboard and the computer confirmed it and even said where it went. If it did so, I think it isn't so crazy to assume that it could do it when they were still on sulaco. The bluray even shows an animation detecting the location of a foreign lifeform. As for Bishop not mentioning neuroscan, I think it can easily be answered by the fact that he was a wreck and accessing such big answers as to if alien was onboard took him some doing