The easiest device to tracks one's HR is the heart rate monitor, that measures the electrical activity of your heart and shows the number of beats per minute. It helps target your training to the best and track your progress.
Originally developed for medical and professional sport settings, it is now widely used thanks to both its simplicity of use and its purchase price.


The most commonly used technology nowadays is the Bluetooth HRM strap alone (or built in a garment) that is paired with a receptor watch or a smartphone application.      
Optical heart rate watches are also increasingly available. This technology determines your HR at your wrist by measuring the variations in blood pressure in the skin capillaries.


Heart rate monitors being increasingly effective, some of them now also provide heart rate variability (HRV) measurement.          
The HRV refers to the amount of time between two heartbeats, when the HR is fairly stable. This amount of time is slightly irregular and is a reflection of the various systems involved in cardiac regulation.                
A low HRV is associated with significant psychological stress, and is considered as a major factor of increased cardiovascular risk, of cardiac incident and of sudden death. It is also provides some insight on the level of fatigue and the quality of sleep.