Sony showed off a prototype tennis racket sensor at CES 2014 that promised to track useful data about your technique and transmit it to your smartphone. That prototype has turned into reality faster than we thought it might — the final product now has a name, a price, and a release date for Japan. The Smart Tennis Sensor is set to hit store shelves at the end of May for an expected price of under 18,000 yen, or about $175.

The Smart Tennis Sensor weighs eight grams, measures 17.6mm tall, and is 31.3mm in diameter, meaning that it shouldn't add much bulk to your racket; compatibility is restricted to six Yonex models at launch, however.

But if the sensor works as well as Sony says, it could be a really useful training tool for Roger Federer wannabes — it measures the speed of your swing, the speed of the ball, where the ball makes contact with the racket, and what kind of stroke you're playing, all of which can be viewed in time with video footage recorded through the app. There's no word on a release outside of Japan for now.