The TomTom Runner Cardio is a heart rate monitor, running trainer, and GPS watch all in one. The optical heart rate sensor on the backside of the watch allows you to accurately monitor your heart rate without the need of a chest strap. You can set your goal within five preset heart rate training zones to get the most out of your work out. The extra large display shows you real time metrics including your calories burned, steps taken, speed, and distance traveled.