Apple wireless mouse devices have a built-in passcode of "0000" (four zeros). If configuration software asks you for a passcode, enter this value.
What is the passcode for an Apple wireless mouse?
Apple wireless mouse devices don't usually require a passcode, but some software requires a passcode to enable the mouse. For example, if you are using your Apple wireless mouse with Boot Camp, the generic class driver in Windows may ask for a passcode.