I recently bought a Polar S625X Heart Rate Monitor. I love it.
My stationary bike has a heart rate monitor built in. But I wanted to be able to monitor my heart rate while doing other exercises. I also wanted something that would help me stay in the right heart rate zones while doing interval training. And I wanted to be able to download the heart rate data to my computer and track my workouts over time.
I knew I'd be getting a bike, ideally I wanted a heart rate monitor that would help my track my cycling workouts too. I also wanted something to help me track running and swimming workouts.
The S625X fit the bill perfectly. It comes with a foot pod that you attach to your shoe. The foot pod monitors your steps so the heart rate monitor can track how fast you are walking or running and how far you have traveled. That makes the S625X a heart rate monitor and a running computer combined.
The foot pod is water resistant so you can use it in the rain. It is surprising light weight so you don't notice it on your shoe.
The accuracy of the foot pod technology isn't perfect. It is best to attach it to your shoe the same way every time you use it. And you should also calibrate it. Even then it isn't perfect. But it is good enough for my purposes.
The S625X is also water resistant to 30 meters. So you can use the watch and the heart rate transmitter in the pool. Heart Rate monitors don't always work for all people in the pool. I haven't tested mine in the pool yet so I'm not sure if it will work for me or not. But even if the heart rate monitor doesn't work while I'm swimming I can still use the stopwatch features on the watch to track my swim workouts.
The S625X can also be used as a cycling computer. You can purchase the speed sensor to track the speed and distance of your cycling workouts. You can add the cadence sensor to monitor your pedaling rate. Those sensors cost about $40 each. There is also a power meter available that let's you monitor the power you are producing on the bike. But that is much more expensive at about $350.
The S625X can communicate with your computer using infrared or sound. It comes with Polar Precision Performance (PPP) software that lets track your workouts.
So far I'm very happy with the S625X. I just got the speed sensor and the cadence sensor for my bike. They both work well. The foot pod works well enough. I could have gotten a GPS based heart rate monitor. But the GPS monitors are much bigger than the S625X. And I have plenty of experience with GPS and I know how unreliable it can be in certain situations.