Pattern Lock.

Maze Lock is a fantastic free software designed to add pattern lock feature to Windows operating system. As with the case of screen savers, Maze Lock gets activated after a pre-defined time of system inactivity and locks down your PC (of course, manual lock is also available). To unlock the PC, you need to draw the pattern that you have set using the mouse.
And when someone tries to unlock your PC with a wrong pattern, it alerts you with an alert sound and locks down the system again.
With default settings, Maze Lock automatically locks your screen after 3 minutes and turns off the monitor after 5 minutes. You can change these default settings by right-clicking on Maze Lock icon in system tray and then clicking Configure option.