A portable electronic device includes a wireless communication module, a processing unit, a display device and a backlight driver. The wireless communication module wirelessly collects location information from at least one remote station. The processing unit executes a positioning application and thereby calculates a position of the portable electronic device based on the collected location information. The display device operates at a bright mode when the calculated position indicates that the portable electronic device is kept being moved. The backlight driver is coupled to the processing unit, and, the processing unit is further configured to control the backlight driver to make the display device leave the bright mode and enter a dim mode when the calculated position indicates that the portable electronic device is not moved for a first predetermined time period.