Working out with a heart rate monitor watch is a terrific way to make sure that you maintain a consistent level of intensity throughout your entire session. What matters in exercise isn’t just the number of repetitions you perform during a session, or how much distance you run or swim, but how long you keep a given exertion level going during that time. Running the same number of miles is half the workout if you take twice as long.

A wrist heart rate monitor lets you know when you’re maintaining your effort by alerting you when you’re not. When you get a heart rate monitor (HRM) watch, the first thing you do is input your date of birth. This tells the watch the maximum allowable heart rate for your age group, as predetermined by professionals. Then you set your desired aerobic zone, which is a range of percentages of your maximum heart rate.

In other words, if you want a relatively light workout, you can set it for between 50% and 60% of your maximum rate. If you want a more intense workout, you can set it between 70% and 85%. Whenever you fail to push yourself hard enough, or you push yourself too hard, the watch will beep continually until you return to your aerobic zone. You don’t have to keep looking at the watch during the workout to get the benefit.

If you work out in a crowded gym, consider one of the more advanced HRM watches from manufacturers like Suunto or Polar. Most of their watches accept coded transmissions from the chest straps they use. If other gym members are using a wrist heart rate monitor while you’re using yours, there’s a tendency for the transmissions to create interference, and you may not get a reading at all. A coded transmitter sends the heart rate information to the watch on a custom channel, so that interference is avoided.

If you work out by yourself, you don’t need this advanced feature. Consider getting one of the simpler Timex or Mio watch products, which offer the basic aerobic zone functionality without the higher price tag. You’ll miss features like computer connectivity (which uploads your workout information to special training websites), but for many exercisers who aren’t competitive athletes, the advanced bells and whistles are overkill. In many cases, the learning curve of too many features prevents new adopters from actually using their devices. It’s best to start simple.