Source: Exotic engrams; extremely rare world drops.
Lore
"If you were rich, what would you do with all your money?" "Uh… I dunno. Maybe start my own business. Be some kinda bounty hunter." "What you mean, bounty hunter? We got thousands of Guardians running around, bounty-hunting anything that moves!" "Nuh-uh! That's all just sport. Them Awoken out in the Reef, I figure they might pay me to hunt folks down. And I got a secret. It's gonna gimme a real leg up on all them Guardians who come to copycat me when they see what a good idea I got." "Yeah? What is it?" "This Hunter, she sold me a visor that lets you find all the stupid enemies in a crowd. Called it 'knucklehead radar' or something like that." "Huh. How's it work?" "Couldn't tell ya."