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This scary AI recognizes passwords by the sound of your typing
(www.pcworld.com)
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Try this: on any keyboard (a membrane keyboard especially if you have one) try quickly tapping one key 3 times and then another key 3 times. Move around the keyboard or alternate between two letters.
Can you hear that they make different sounds, but typing the same letter has roughly the same sound? The" plok" has a higher or lower pitch (frequency is the scientific word for it), and a trained AI can match that pitch to a letter if it has or can get an idea of what corresponds to what.