Smash is crowdfunding its gadget with hopes of shipping it in February. If you're looking to improve your game, it'll currently take a $129 Australian pledge ($119 US plus $10 in shipping) to get the finished wearable; wait until the planned release and the device will set you back $199 AUD ($184 US). That's as much as some nicer general-purpose fitness trackers, but it may be justified if you absolutely have to be victorious on the tennis court.