Turns off all monitors in Windows using the Win32 API.

monitor-off.rbw

# Send all monitors to power saving mode (standby) using the WIN32 API.
#
# Documentation for WM_SYSCOMMAND & SC_MONITORPOWER:
# http://msdn.microsoft.com/en-us/library/windows/desktop/ms646360(v=vs.85).aspx
require 'fiddle'
require 'fiddle/import'
require 'fiddle/types'

module User32
  extend Fiddle::Importer
  dlload 'user32'

  include Fiddle::Win32Types
  extern 'ULONG SendMessage(HWND, UINT, UINT, ULONG)'
end

HWND_BROADCAST  = 0xFFFF
WM_SYSCOMMAND   = 0x0112
SC_MONITORPOWER = 0xf170

POWER_LOW = 1
POWER_OFF = 2

User32.SendMessage(HWND_BROADCAST, WM_SYSCOMMAND, SC_MONITORPOWER, POWER_OFF)