Notch Body Tracker
Instead of wearing just one device to track motion, Notch can be used in tandem with multiple trackers to gather even more detailed data. Number of steps in a day are useful, but Notch goes beyond that, tracking speed, acceleration, and force.
The extremely small, Bluetooth-enabled device integrates with "movement-capture apparel" that has Notch mounts in each limb to collect information about the angle of a knee or the movement of a hip, for example.
It's great for martial artists who want more info about the speed of their kicks or tennis players who'd like to measure how fast their serves are.