Simple - asks for three pin numbers, verifies them as you enter them, and if correct, lets you in.
Move PIN command to /usr/bin (or wherever your shell gets it's commands).
Use konsolelock.c as your configger. Change the variable test-for numbers on the while loops and you've set the PINs. Use your compiler then move a.out to ~/pin.out (where the pin command looks for your pin config.)