*#*#7594#*#*
This one is my favorite one. This code can be used to
change the "End Call / Power" button action in your phone. Be default, if
you long press the button, it shows a screen asking you to select any option
from Silent mode, AirPlane mode and Power off.
You can change this action using this code. You can
enable direct power off on this button so you don't need to waste your time in
selecting the option.