I am a big advocate of Heart Rate Training and one of the questions that comes up often is "What should I look for in a Heart Rate Monitor"?
Here are my top four points to consider when deciding the best heart rate monitor (HRM) for you:
1. HRM's with chest strap and watch tend to be more accurate than wrist or thumb versions.
2. A chest strap can also be detected by modern cardio equipment so HR is displayed on the console monitor. This can be useful when exercising at gyms.
3. Is the chest strap battery accessible? i.e. Polar have sealed units so when the battery runs out you have to send in the chest strap for a battery replacement. Other models such as Beurer, Reebok, Timex allow access the battery so you can replace it yourself.
4. Choose one with a large HR display so you can read it easily when exercising.
I find the Beurer Award Winning HRM's with their "German precision" to be very reliable:
Finally, unless you are an athlete or serious runner/triathlete, buy the one with the least features (also happens to be the cheapest). You will find you only use the HR reading and maybe setting upper and lower limits if preferred. Most people waste their money by buying too many features that they never use.