Detecting screensaver state in Ruby with DBus...

dbus.rb

#!/usr/bin/env ruby
# encoding: utf-8

require 'time'
require 'dbus'

main = DBus::Main.new
trap("INT") {
  puts "Quitting..."
  main.quit
  exit
}

bus   = DBus.session_bus
saver = bus.service("org.gnome.ScreenSaver").object("/org/gnome/ScreenSaver")
saver.introspect
saver.default_iface = 'org.gnome.ScreenSaver'

saver.on_signal("ActiveChanged") do |state|
  str = state ? 'activated' : 'deactivated'
  puts "[#{ Time.now } ] Screensaver has been #{ str }."
end

main << bus
main.run