With the US Open drawing near, you should probably start working on your serve so you can compete alongside the pros from the comfort of your own court. Whatever your weakness is, whether it be your serve or backhand, Zepp Tennis can help. Much like the sensors designed to better your golf swing, just attach Zepp to the handle of your tennis racket and play. The gadget collects 3D data in real time and sends it to the accompanying app on your smartphone or tablet, measuring things like racket and ball speed, spin, backswing time, and impact time. There's even a "sweet spot" feature that shows you exactly where the racket makes contact with the ball, which helps you with quality and consistency. Zepp may or may not turn you into the next Novak Djokovic, but it will definitely help you get closer.