(being aware of how unlikely such thing is to happen) did a little sketch for an alien detector (attached).
the idea is that some scientist measured nerve signals in alien brain, and discovered that it responds to other alien's presence.
so, the device has a piece of alien brain inside a vial with nutrient solution that keeps it functional.
a live alien could be a component needed to manufacture the detector (or alternatively, to "recharge" it before battle, but that might get complicated and increase micromanagement).
detects aliens as a number, which is sum of alien max health points divided by distance.
so the player can no longer see through walls, but gets "warmer-colder" type of hints about the location of aliens.
that would look like a (imho necessary) downgrade, but on the other hand it detects aliens all over the map, so no more running around with goggles looking for the last alien.