I'd been going to the gym for 3 months when I decided to take the plunge and buy myself a Polar FT4 heart rate monitor after seeing so many pictures of them dotted across Instagram and the fitness blogs I follow. The Polar FT4 measures your heart rate during exercise, and also calculates your calories which are displayed on the watch.
It's completely un-obtrustive to wear, and I don't even feel the chest strap (which is how your heart rate is measured) whilst I'm wearing it. The watch is small and lightweight, meaning it doesn't get in the way, but the screen is a good size and easy to read at a glance. I love that you can alternate the screen between displaying your heart rate, calories or work out time - I actually use the clock on it a lot to time intervals on the spin bike.
The big question everyone asks is if it works, and if it's an accurate gauge of calories burned. I done a lot of research before buying, and I also spoke to my personal trainer about it to get a professional opinion. The long story short is that although it won't be 100% accurate when it comes to counting calories burned (nothing ever is), it's pretty close as it uses a formula made up of your height, weight, age, sex and heart rate. It's definitely a whole lot more accurate than the equipment at the gym, and calorie counting aside, it's main purpose of tracking your heart rate gives a good indication of your, hopefully improving, fitness level.
One thing I am a bit dubious about is the fat burning zone. The watch uses another formula to work out a zone, which is between a certain heart rate range, where your body burns the most fat. The downside is that for me, whilst doing cardio, the 'fat burning zone' leaves me feeling like I'm barely working hard, and at the end of the session I've burned a lot less calories and barely broken a sweat. Again, after doing some research (my god, everything fitness related is so controversial!) and reading this article I personally think I will ignore the fat burning zone suggestion and stick to working as hard as I can!
I find that wearing my Polar FT4 really motivates me to push harder at the gym, and often find myself looking at it and seeing 745 calories burned, for example, and telling myself that I'm not getting off the bike until I've rounded that figure off to 800. I love setting myself mini goals for calorie burns to keep myself motivated on tougher days at the gym when I'd rather be elsewhere. And lets not forget the days where I've indulged a few treats - seeing the calories of that chocolate bar add up on my watch is such a good feeling!
If you're serious about fitness then I'd definitely recommend one of these - I definitely feel the difference in my mood and motivation levels if I forget to bring mine to the gym.