Wow man how to do this! Simple, just one line of code to send your monitor into standby mode.
::PostMessage( m_hWnd, WM_SYSCOMMAND, SC_MONITORPOWER, 2 );
Do this using a timer and you will have your monitor turned off every 1 second which prevents anyone from turning your monitor on because it goes into standby mode every 1 second ;).
It’s not that secure but still it’s fun or use this to trick your IT friends! 🙂