Gem of Seeing
Very rare wondrous item
Property: As an action, you can peer through the gemstone. You automatically spot hidden or invisible creatures or objects within your line of sight. In addition, you automatically recognize creatures or objects created by illusions as illusions. You can also see into the Astral Plane and the Ethereal Plane.
Secret: A character who uses a gem of seeing has a 5 percent chance with each use of seeing a hallucination or mistaking a real object for an illusion.
This finely cut and polished diamond is the size of a human eye. A creature that holds a gem of seeing to its eye notices that the gem is transparent, and peering through it in no way blurs or distorts the creature’s vision. One can turn a gem of seeing into a pendant by setting it in a loop of metal, so that the gem is always within easy reach and hard to lose. A dread pirate lord had one set in an ornate eye patch.