Gem of Seeing

From Dungeon Master's Guide, page 172. Found on Magic Item Table G.

Description
''Wondrous item, rare (requires attunement). 1 lbs.''

This gem has 3 charges. As an action, you can speak the gem's command word and expend 1 charge. For the next 10 minutes, you have truesight out to 120 feet when you peer through the gem.

The gem regains 1d3 expended charges daily at dawn.