This multifaceted diamond is usually placed in the eye socket of a statue or an idol, or atop a tripod that overlooks a room. It sees all and reports back to its master what it learns.
Wondrous Item 325,000 gp
This eye can see invisible creatures and objects within 20 squares of it. When a creature enters the eye’s line of sight, the eye telepathically warns its owner of the creature’s presence and provides a description. It can communicate with its owner across planar boundaries.
Published in Adventurer's Vault 2, page(s) 79.