The Fitbit Charge 4 is the successor to the popular Charge 3. Although there are few differences, new features have been added. For example, the Charge 4 has an integrated GPS receiver to measure your speed, distance, and route without using the GPS signal from your smartphone. You can leave your smartphone at home during a run. The activity tracker also has Fitbit Pay. With this, you can make contactless payments if your bank supports Fitbit Pay.