zlacker

This has been a known/practical attack for decades. OTOH, it does require physical proximity, although you could probably do it with a remotely controlled sensor at an intermediate location near the target.

What would be terrifying would be if someone could figure out how to do this attack via software compromise of some hardware sensor system already present throughout the environment; say, a way to repurpose a wifi chipset to pick up nth-order harmonics off a keyboard bus or something. Then, remote-root of some lesser machine could be used to spy on a hardened machine.

>>rdl+(OP)
That was done a couple years ago

"IN THE AGE of surveillance paranoia, most smartphone users know better than to give a random app or website permission to use their device’s microphone. But researchers have found there’s another, little-considered sensor in modern phones that can also listen in on their conversations. And it doesn’t even need to ask."

http://www.wired.com/2014/08/gyroscope-listening-hack/