The sound comes from Portal, the first person puzzle game released by Valve in 2007 as part of The Orange Box. Its Sentry Turrets are white, tripod Aperture Science machines voiced by Ellen McLain, the same actor behind GLaDOS. Their sweet, pre recorded warnings became one of the game's most quoted features, spreading through gameplay videos, remixes and gaming memes long after release. Because the voice is instantly linked to being spotted by a machine, creators still use it as shorthand for automated surveillance and polite menace.