Wearable tech has come a long way in a relatively short space of time. Two decades ago, recording your heart rate meant being wired up to an ECG machine, or wearing a chest strap 24/7. Now your smartwatch can do it with a tap – and throws in step count, blood oxygen levels and a sleep report for good measure. Today’s fitness trackers are stuffed full of sensors and can accurately chart hundreds of different sports, activities, and exercises.