You will never get a key code for an *ALT* arrow keypress. This is because
ALT NUM-PAD keys is untercepted and interpreted as an ascii code for a
character input (eg ALT-6,5 will generate 'A' or keycode 0x0041), Perhaps if
you write your own keyboard interrupt handler to avoid the interception.
Alternatively, you can make do with Ctrl-Cursor-key, or Shift-Cursor-key.