Keypad security door lock...?

i am making a keypad security door lock using the microcontroller 89c51. in this the password is entered by the user. the microcontroller matches the password with the default password if it is correct the door opens. the problem is i want to introduce the feature to change the default password. in other words the... show more i am making a keypad security door lock using the microcontroller 89c51. in this the password is entered by the user. the microcontroller matches the password with the default password if it is correct the door opens. the problem is i want to introduce the feature to change the default password. in other words the user should be able to set the default password of his on will. how can i do it.? another thing if the microcontroller is turned off the changed password will remain in the microcontroller and user can enter the new password to open the door. thank you
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