Newer iPhones come with a chip called a motion coprocessor which gathers data from the accelerometers, gyroscopes and compasses of the device to precisely measure motion and fitness data such as body motion, step count, stairs climbed, and more. Most people, including yours truly, do appreciate the data collected as it's particularly helpful if you want to use your iPhone as a step counter and pedometer, for instance. Others are creeped out by this feature.
If you belong to the latter group of people, then I will show you a quick and easy way to stop your iPhone from tracking your steps and other fitness activity.