A mobile electronic device, an early warning method and an early warning system for assisting users in actions are provided. The mobile electronic device includes a distance sensing module, a controlling module. The distance sensing module obtains first distance information. The controlling module calculates a user height according to the first distance information, calculates a calibration angle according to the user height and a safety range, and obtains second distance information through the distance sensing module after rotating the distance sensing module according to the calibration angle. The controlling module determines whether the second distance information complies a criteria condition. If the answer is yes, then a warning message is outputted. Accordingly, dangling objects can be detected to remind a user that an obstacle is near around.本發明提出一種輔助行動的行動式電子裝置、預警方法與預警系統。此行動式電子裝置包括距離感測模組與控制模組。距離感測模組是用以取得第一距離資訊。控制模組是用以根據第一距離資訊計算出使用者高度,並根據使用者高度與安全距離計算出校準角度,根據校準角度旋轉距離感測模組後透過該距離感測模組取得第二距離資訊。控制模組判斷此第二距離資訊是否符合臨界條件,若是則發出警告訊息。藉此,可以偵測到懸空物,以提醒使用者周圍有障礙物。S701~S705‧‧‧步驟
