“Here you can see how the "sunglasses" work”
Scene showing how the sunglasses in They Live work.
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Found it: "They Live" by John Carpenter. The idea is a bit different though. "Nada discovers the sunglasses are special. After putting on a pair, he sees the world in black and white and discovers it is not what it seems. Media and advertising hide constant subliminal totalitarian commands to obey and conform." ( link ) Here you can see how the "sunglasses" work: this video [Added additional information]