In 2010, Microsoft popularized gesture controls with the release of the Kinect. In its first 60 days on sale, the device sold 133,000 units per day, a Guinness World Record. Three years later, Leap Motion brought the same capabilities to personal computers. But both devices required stationary sensors to perceive movements, so users couldn’t stray too far. Now, a new set of devices—outfitted with ultrasound, electromyography (EMG) sensors, and inertial sensors—are allowing the use of touchless interfaces anywhere.