One of my must haves while I am exercising is my heart rate monitor watch by Nike. The monitor I have is the women's Nike Imara HRM. It comes in a set which includes the watch and a chest strap.
The watch can be worn alone if you just want to tell the time or set workout intervals. When you want to know your heart rate and in turn calculate how many calories you've burned during your workout, you then strap on the chest strap. There are sensors on the chest strap that transmit to the watch and the watch then tells you what heart rate you're at. What I think is really neat is you can set the watch to beep when you are out of your target heart rate zone, or above your max heart rate.
The one I got is ice blue in color, I love it! To calculate your calories you just have to input your weight and age into the watch and it will compute it from that factoring in your heart rate. It keeps this set age and weight in the watch until you change it. So if you are trying to lose weight, I would definitely change your weight accordingly. If you don't do that you won't get as accurate details on your workout data as you should.
Overall I love this watch and I think it's a great asset for anyone that wants to keep track of their heart rate. It really lets me know when I need to work harder, even if I feel like I've given it my all already!
Oh and before I forget, if you use this while you are on a workout machine like a treadmill or an elliptical that can track calories and heart rate, it will pick up the signal from your chest strap and relay it to you through the machine. Very neat!