From All About Circuits: Google ATAP is bringing touchless interfaces to the market using a miniaturized radar chip no bigger than a dime. This is Project Soli.
Soli’s radar sensor is a marvel in many respects. For one thing, it solves a long-lived issue when it comes to gesture-recognition technology. Previous forays into the topic yielded almost-answers such as stereo cameras (which have difficulty understanding the overlap of fingers, e.g.) and capacitive touch sensing(which struggles to interpret motion in a 3D context).
Google ATAP’s answer is radar.
Radar is capable of interpreting objects’ position and motion even through other objects, making it perfect for developing a sensor that can be embedded in different kinds of devices like smartphones... (full article)
Vert-X 05E Series of dual angle/speed sensors. The series features easy mounting in small and narrow spaces with a 5 mm body depth and mounting flanges with metal inserts. The sensors make measurements only 6 mm from edge of product for close-to-wall measurement applications. Vert-X 05E Series sensors measure angles from 0 to 360°, rotational speed and direction with repeatability to 0.1°.