A door lock includes a latch device and inner and outer operating devices operatively connected to the latch device. The inner operating device includes a control module and a first battery module electrically connected to the control module and supplying electricity for operation of the door lock. A detecting module is electrically connected between the first battery module and the control module. The outer operating device includes a first electric connecting device electrically connected to the detecting module and an unlocking information input module electrically connected to the control module. When the remaining electricity of the first battery module detected by the detecting module is lower than a preset alarm value and a second electric connecting device of a mobile device is in electrical connection with the first electric connecting device, the second battery module of the mobile device supplies electricity to the door lock for operation.