A mobile device is provided. The mobile device includes a transceiver, a sensor unit, a storage device and a processor. The sensor unit detects the position and the motion of the mobile device to provide sensor data. The storage device stores activity records. The processor obtains an identification code of the base station connected to the mobile device through the transceiver and calculates the height of the mobile device according to the sensor data. When the identification code of the base station and the height of the mobile device match those in an activity record, the processor executes a predetermined function corresponding to the activity record. When the execution of the predetermined function fails, the processor generates a moving trail of the mobile device according to the sensor data. When the moving trail of the mobile device matches that in the activity record, the processor executes the predetermined function.