Moov
Most fitness trackers are designed only to record your activity, measuring your movement throughout the day and maybe even supplying some performance metrics. The Moov can certainly do all that, but it serves as a personal trainer, too. By pairing either one or two of the waterproof 9-axis motion sensors — the number depends on the activity you're doing — with your phone over Bluetooth 4.0, the companion app is able to give you audio and visual instructions while you're working out, serving as a virtual personal trainer, and helping you to maximize your efforts while avoiding injury.