A gyroscope is simply a device that uses the earth’s gravity to determine orientation. Use of a gyroscope function in a fitness tracker helps enable the device to show how much activity you are actually doing. Since a gyroscope can sense rotation. Watch or Activity Monitors that are capable of tracking your movements during your sleep make use of the gyroscope functionality to measure how much you twist and turn during night’s sleep, like the Fitbit and Fitbit Charge.