A temperature key includes a temperature sensor, a microprocessor chip, a storage device, a port, a record button and an enter button. When the temperature key is connected to a computing device and the record button is pressed, the temperature sensor is triggered to record a temperature signal input by a user. The microprocessor chip converts the temperature signal into a password, stores the password in the storage device, and sends the password to the computing device to lock the computing device. When the temperature key is connected to the computing device again and the enter button is pressed, the microprocessor chip retrieves the password from the storage device and sends the password to the computing device. The computing device is unlocked in response to determining that the received password matches the password stored in the computing device.