The Detect Hidden skill is used to reveal Players that have been hidden from normal sight using either magic or the Stealth Skill. It is particularly useful for tracking down players with bounties.

Detect Hidden is a passive skill that can be unlocked from Inspector Gidget around level 100.

When you have Detect Hidden you do not need to do anything, it will automatically work to show you stealthed players. You can not "unstealth" them but you can interact with them as if they were not stealthed.