Do Aliens have…eyes?
If you mean the aliens from the Alien movies, then no, they don’t.
They have eye sockets in their skulls, but have a smooth covering over their heads. Maybe they have eyes that look through a transparent carapace. Who knows?
I’ll bet they haven’t thought it out.
In any event, (apparently) eyeless creatures that can tell where you are can be incredibly creepy, and show up in horror novels and movies a lot. see Alan Garner’s The Weirdstone of Brisingamen, for instance.
Lots of 'em out there: http://tvtropes.org/pmwiki/pmwiki.php/Main/EyelessFace
The graboids from Tremors.
Composite eye that blends with the carapace, sensitive to the infrared spectrum?
Simple: it relies on directions
Alien 3 had several scenes shown through the creature’s eyes.
https://youtu.be/kPfEEJ5aG10?t=15s
Good list of Earth animals with odd eye functions and eye appearances here. 10 Animals With Incredible Eyes - Listverse
Assume that a xenomorph’s eyes are like a trilobite’s or spook fish’s eyes.
H.R. Giger used a human skull to make the prototype of the alien head, but deliberately designed not to have visible eyes. His thinking was that it appeared more menacing that way.
I thought it was to make it more closely resemble a penis
Perhaps it’s kinda like the barreleye fish, which has huge, upward-looking tubular eyes inside a transparent dome-like head, only that the carapace isn’t transparent in the (human) visual range.
At least oneXenomorph skull that we’ve seen, however, appears to to have solid bone over the frontal “dome” of the carapace. Vagaries of the canon, the creatures’ anatomy and genetic traits (they are known to adapt at least some of their host-species’ biology into their own adult forms, and there might be many thousands of years of genetic separation between Xenomorph strains), and even the effects of Predator trophy-preservation techniques might not make this a definitive answer.
The Colonial Marines Technical Manual has a neat section transcribing some Weyland-Yutani scientist/executives puzzling over the fragmentary information they’d recovered from LV-426, trying to figure out Xenomorph anatomy, including their sensory systems. There’s speculation at one point, IIRC, that the Xenomorphs’ elongated heads were part of a complex auditory system, if not true echolocation, that they used instead of actual vision.