Equip: Improves hit rating by 21. Equip: Improves critical strike rating by 38. Equip: Increases attack power by 108. Use: Shows the location of all nearby demons on the minimap until cancelled. Only one type of tracking can be used at a time.
This helm - a blindfold worn over the eyes - appears to be that worn by Illidan himself.
Origin
When Illidan joined forces with the Burning Legion in the War of the Ancients trilogy, Sargeras "gifted" him with new vision. He did this by burning his eyes from his skull and replacing them with an ability to see the magic in existence all throughout Kalimdor. Because the sight of his empty eye sockets was unnerving and displeasing to Azshara and her Highborne, and because it did not impede his magical vision, Illidan was given an amber cloth which he tied around his head over his eyes.
As it's the new eyes given by Sargeras that granted him a new vision, it seems to be a mistake that Illidan's bandana allows players to see demons. See : Illidan's Bandana Retcon