From our discussions with people who have never used a heart rate monitor, we find there is confusion about what they do and how they work. Many have seen ads showing wristwatch style monitors and think that these detect pulse from the wrist with no external wires or sensors. Unfortunately there is no monitor capable of detecting heart rate from the the wrist. Further confusion is caused by advertisements for monitors that require holding a finger on a sensor on the face of the watch. The advertisements do not make it clear that the user must stop exercising and hold their finger on the sensor and be very still, while measuring. Thus readers of these ads think these monitors will measure heart rate continuously while exercising. Such is not the case.

All heart rate monitors have a means of detecting the heart beat and sending an electrical signal with each beat to the electronic circuitry of the monitor. A timing circuit measures the interval between each beat, averages the intervals for a short period of time and converts this into a heart rate reading expressed in beats per minute. The readout does not display the equivalent heart rate for each individual beat because the heart is not a mechanical device like a clock pendulum, and the interval between beats varies. If the rate for each beat were displayed successively, the number would change with each beat. For example, if a persons average heart rate during exercise were 142 beats per minute, and the monitor displayed the rate for each beat, the readings might read: 145, 141, 138, 143, 142, 147, 141, 137, 140, 144, etc. Readings like this, changing with each beat, would be difficult to read and follow. To overcome this, monitors average for a period of time, typically 5 to 15 seconds depending on the model. Thus, the heart rate reading shows this average and remains steady until updated with the next average.

The most significant difference among all heart rate monitors is the method used to detect the pulse or heart signal. There are three main systems in use: 1. detecting blood flow in the capillaries of a finger or ear lobe with an infrared sensor; 2. detecting the heart EKG electrical signal in the hand area, and; 3. detecting the heart EKG electrical signal with chest electrodes, commonly attached to an elastic strap going around the chest.

Each of these systems has its own advantages and disadvantages. The following page has a description of each type of heart rate monitor: