Metrocops are the Combine Civil Protection officers in Valve's Half-Life 2, released in 2004, who patrol City 17 and speak through distorted radios and masks. When one is killed in the game, its voice unit emits this collapsing electronic noise, a cue players learn to associate with clearing a patrol. Fans later ripped and shared the game's audio on soundboards, where the clip took on a second life outside gameplay, especially in Half-Life and Garry's Mod edits that needed a quick, recognisable robotic death.