I wanted to propose an item that allows you to see through walls (and machinery). It could be explained as a specialized retina that detects a wide spectrum of light (such as infrared, X-rays, gamma rays, etc...), including "light" that is not easily stopped by the material of Complex' walls.
I can imagine that seeing through walls at your usual view range would be quite OP. If X-Ray Retina (or whatever it will be called) were a common item, then seeing through walls at a range of only 5 would already be usable to find where you can dig safely (comparable to a terrain scanning setup) and would warn you against hostiles in a room (comparable to sensor setup). So some limitations should be applied, such as:
- range limitation, e.g. only sees stuff at a range up to ~5.
- multislot/heavy/high energy cost/etc.
- is still blocked by earth tiles
- only sees through up to X wall/earth tiles
- doesn't see everything (terrain, items, robots, machinery); e.g. can't see terrain (if it can see through terrain, then it can't see the terrain itself)
And of course there is an option to allow it to be OP, with range equal to your visual range, further enhanced by optical arrays. If it's a rare unique part, it might be fine.