Two clicks on the back shell of the Mi 13 phone means that a specific function can be quickly called out by double-clicking the back shell, which can be opened and set in the Settings. The specific operation steps are as follows: open the \"Settings\" menu of the phone, find the \"Additional functions\" option, click to enter the \"double-click on the back shell to wake up\" function, you can select the application or function that needs to be quickly called up after opening. For example, select \"Camera\" to bring up the camera function by double-clicking the back shell on the lock screen. It should be noted that this function requires the support of the phone's back shell to be used.