It's tough to keep a gun drawn on a prisoner when the cell door lock requires two hands to open - that's where the Key Gun comes in. It's literally both a key AND a gun. Our friends at Oobject have six classic examples.
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Why Isn't Close Encounters Considered Steven Spielberg's Ultimate Masterpiece? Because It Kind of Is
Well, hand-guns don't really shoot hands now, do they?
(not that I'm saying it wouldn't be awesome if they did)