Tracking Your Heart Rate
Heart rate tracking has been around for a while and many people will be familiar with a chest band that is worn during an exercise activity. More recently, new sensors have been developed and incorporated into Fitness Trackers that through their low power usage and more convenient fitment means that your Heart Rate can now be tracked 24hrs a day.
The two sensors work in very different ways. The older chest band type monitor the electrical pulses when your heart beats whilst the new sensors monitor the small changes in your skin colour as blood moves around your body.
Getting good readings from the two types of sensors needs a bit of understanding. The chest band type needs good skin contact to get a good electrical signal and needs to be fairly tight (uncomfortably tight for some users). However, the new light based sensors do not need to be tight to your skin. If this type of sensor is too tight it will squash the blood vessels in your skin and the sensor will have nothing to read and you'll get poor readings.
Knowing your Heart Rate allows the Trackers to see how hard you are working during exercise so will allow you to see if you are finding things too comfortable. Your Heart rate will also allow you to train in the right "Zone", ie. Fat Burn or Aerobic zones.
As the Fitness Trackers are working all day long they can better show you your "resting" heart rate, this can help you see if your body has recovered after heavy exercise or needs more time (if you HR is higher than normal then your body may still be repairing itself). They can also show you which activities or situations during your day cause your heart rate to rise.
In terms of accuracy, there seems to be a prevailing view that the chest band type are ultimately more accurate particularly at high Heart Rates for activities, whilst the light based sensors are fine at low to medium Heart Rates but accuracy may tail off at higher rates. I don't have an opinion on this or any evidence to support a view one way or another.