In case you're not familiar with heart rate monitors, they usually come with a watch you wear on your wrist, and a chest strap transmitter that you wear around your chest, since it is after all a chest strap. This strap goes next to your skin (sometimes you have to wet it a little with saliva or water to activate it) and it reads your heart rate and transmits the beats per minute to the watch.
Heart rate monitors can be expensive, depending on how many bells and whistles you get, but these strappy heart rate monitors will give you a constant readout of your heart rate, whether you're moving or not.
Then there are STRAPLESS heart rate monitors, like this one from Reebok called the Fitwatch 10S Strapless Heart Rate Monitor Watch. Don't be fooled! These sound innovative and amazing, but here's the deal. They don't give you a continuous readout. You see those two little grey buttons above and below the screen? You have to stop moving and stand still, press down on those buttons, and after 2-10 seconds, it'll tell you what your heart rate is.
These may not be good for people who have low resting heart rates, irregular heartbeats, or poor circulation in your fingertips.
You may be okay with having to stop every time to check your heart rate just so you don't have to deal with that annoying and constricting chest strap (that can slide down your torso when you get sweaty). If that's the case, this Reebok model got some great reviews. It's easy to use, gives you just as accurate a reading as strappy heart rate monitors, looks more sleek and feminine than other bulky watches, and is only $63.07 through Amazon.