In the extras I think it was mentioned they blagged from a major rock group whatever lasers they had for the concert stage. But... Since the alien movie has been remastered more than any other of the franchise films, with plenty of opportunities to correct or digitally enhance scenes, I think we'd have to assume only having 1 laser beam covering one section of the derelict was intentional and not due to lack of resources.
However, Kane lowered himself into an accidental acid blood burn hole. Where Kane landed is not the default entrance/starting position for the lower section where the eggs are.
It had to be some kind of sensing laser. Like an outdoor porch light that goes on when movement is detected.
Anyway, I think (and hope) there will be some creature not shown in any of the trailers. Whether it will be the badass or mother-supreme, im not so sure.
