Here is a cool sensor that helps you analyze and improve your tennis game. The Smart Tennis Sensor and app let you view the data from each session and analyze ball impact spot, spin, speed, swing speed, and more. You will be able to see video recorded during play and match it with your data. The device lets you see your data in real time on your smartphone via Bluetooth.
The Smart Tennis Sensor lets you share your progress with your friends. You can use it without a smartphone. It costs under $200 at this time.