But turn spellcheck on, and things get really noisy. The signals can be picked up by an AM radio, Prvulovic said. In fact, the processing is so loud, it's audible: a person can hear it.
Each keystroke causes the spellchecker to look up the word in a dictionary to try to catch a mistake and flag it.
"It turns out that spellchecking is orders of magnitude more activity than you would normally get for just a simple key press," he said. "Modern software does a lot of stuff that is convenient but horribly computationally intensive. That creates differences that can be picked up."
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