Ever find yourself at the end of a workout, and you've barely even broken a sweat? Real-time feedback from a wearable device that tracks heart rate or calories burned may inspire you to push yourself harder. (Plus, you'll feel more connected to your training.) Try the Fitbit Charge HR ($140; amazon.com), Withings Pulse 02 ($100; amazon.com), or the Intel Basis Peak ($173, amazon.com).