The Sense 2 is Fitbit's most advanced fitness tracker to date, and Amazon is offering a chance to snag one for 33% off during this early Black Friday sale. It boasts tons of advanced health metrics, including your stress level, blood-oxygen saturation, an ECG function and much more. And it manages to pack in plenty of handy smartwatch features as well. It has a built-in GPS, can receive call and text notifications, a tap-to-pay function, customizable faces and much more. It's also waterproof up to 50 meters and has an impressive six-day battery life.