Keeper’s Eye

Wondrous item, uncommon (requires attunement)
  Dancing between the rays of moonlight, Heliana ducked, jumped, and rolled her way from shadow to shadow. L’Arsène—ever practical—glanced down at his family heirloom, the keeper’s eye. It was open. “Uh oh,” he thought. “Heliana,” he whispered, “I don’t think we’ve managed to avoid det-” but his call was cut short as a huge, multi-pupiled eye opened at the end of the hallway, six smaller eyes quickly following suit.
  Thief Sense. Not being seen is a real boon for a thief. Moreover, knowing you’ve not been seen is the real decision maker. While wearing this amulet, the eye remains open while you are perceived by one or more creatures using vision or any other sense (such as tremorsense) listed in a creature’s stat block. The eye shuts while you aren’t being perceived. If a creature is suspicious of your presence, but hasn’t yet spotted you (such as if you make a noise), the eye half-opens.
  When you finish a long rest, you can designate any number of creatures that you can see. Those creatures’ perception doesn’t trigger the eye’s magic.