turn_off_monitor.rb

# requiring rubygems is not needed for JRuby
require 'rubygems' unless defined?(JRUBY_VERSION)

require 'ffi'

# Simple FFI module for some low level system commands (on Windows only!):
# * Turn monitor(s) power off
# * Show the Start menu
module SysCommands
  extend FFI::Library

  MONITOR_OFF = 2
  WM_SYSCOMMAND = 0x112
  SC_MONITORPOWER = 0xF170
  SC_TASKLIST = 0xF130

  ffi_lib 'user32'
  ffi_convention :stdcall

  attach_function :FindWindow, :FindWindowA, [:pointer, :pointer], :pointer
  attach_function :SendMessage, :SendMessageA, [:pointer, :int, :int, :int], :int
  attach_function :lock_screen, :LockWorkStation, [], :bool

  def self.turn_off
    hwnd = FindWindow(nil, nil)
    ret = SendMessage(hwnd, WM_SYSCOMMAND, SC_MONITORPOWER, MONITOR_OFF)
    puts "Can't shut down the monitor: Error Status #{ret}" unless ret == 0
  end
  
  def self.start_menu
    hwnd = FindWindow(nil, nil)
    ret = SendMessage(hwnd, WM_SYSCOMMAND, SC_TASKLIST, 0)
    puts "Can't show start menu: Error Status #{ret}" unless ret == 0
  end
  
  def self.lock_and_turn_off
    lock_screen
    turn_off
  end
end

# SysCommands::start_menu
# SysCommands::lock_screen
# SysCommands::turn_off

SysCommands::lock_and_turn_off