From HoNwiki

Bound Eye
Cost
700
Stats
Passive
Modifier
None
Location
Relics
Dota Counterpart
Gem of True Sight

Lore

Through a powerful and religiously suspect ritual learned in part from Beast shamans, it is possible to link a Ward of Revelation to a soldier, creating a Bound Eye that he can carry into battle and use to descry stealthed enemies.

Passive

Reveals invisible units and wards in a 800 unit radius around the holder. Drops upon death.

The More You Know

This item is one of the few that can be shared with allied heroes and still function, so it is common for one player to purchase the item and then hand it to one of his or her more 'tanky' teammates.