Heart rate monitors

I have recently started using a watch that can read my heart rate while I'm exercising.
There are two types of watches: One that has a chest strap, and one that doesn't. The watch with the chest strap measures your heart rate continuously unlike the one without it; I have been using the one with the chest strap. I found it very motivating and helpful. It's very important to know your heart rate per minute in order to improve your shape. The watch tells you the range of the rate that you want to be in, based on the selected exercise; so if it's below the lower range, you would know to increase the exercise and vice versa.

Based on your age, height, weight and gender it also tells you during or after the exercise the amount of calories you burned and the maximum and average rate of the workout. For example, I used it when I was mountain biking for about an hour and a half; it was pretty amazing to see that you burned about 600-700 calories.

And what makes it more like a personal trainer, is that every midnight on Sundays it puts an icon of a trophy if you reached the goal that you previously selected.