Whereas lap swimmers need to know how to do that fancy underwater flip, you open water swimmers want to know your splits, speed, distance, accumulated time and elevation. Just clip a precalibrated Hydro Tracker to your goggle straps and you’re ready to use GPS to track your performance. Its rechargeable battery will keep up with you for 8 to 16 hours, depending on how you adjust the sampling rate. Whether you’re a Mac or PC user, you’ll be able to view and zoom in on your route with online mapping. And the included neoprene armband makes it a natural for tracking the trails you blaze on dry land.