If the people inside the room are close enough to the window, their conversation creates vibrations that the equipment can translate into a crude reconstruction of the conversation, Schmiedl said.
"We're burning the candle at both ends," he said. "The technology is becoming easier and cheaper and anybody can do it. And at the same time there's more incentive now to do it. These are two trains on a collision course. The question is when they're going to collide."