A Universal Serial Bus (USB) flash drive includes an USB interface, a control unit, a storage unit, a timer, a logic circuit, and a quartz meter that includes a scale dial and a dial pointer. The control unit calculates a storage capacity difference between a current storage capacity and a previous storage capacity, and calculates a runtime of the dial pointer according to a time calculation algorithm. The control unit generates an enabling signal if the storage capacity difference is not equal to zero, and generates an interrupt signal when the runtime equals the time value. The logic circuit outputs a high voltage to the quartz meter to control the dial pointer to run around the scale dial according to the enabling signal, and outputs a low voltage to the quartz meter to control the dial pointer to stop running around the scale dial according to the interrupt signal.