Cell phone tracking involves using the data from a phone's Global Positioning System, or GPS, or from cell phone towers the phone connects to in order to determine where the phone is physically located. Installing a tracking app on a phone helps the owner find it if it is stolen or lost. Law enforcement may also track phones in circumstances in which a crime or other issue is suspected.
People who use cell phone tracking apps usually visit a website to see the lost or stolen phone's location, and there are usually options to sound a loud alarm. If no tracking app was installed on the device, there are options like Plan B for Android, which is an app that can be downloaded to the phone remotely, or Find My iPhone, which is pre-installed on all iPhones with at least iOS 5.