We just checked into our hotel in Palma and one of the first things I noticed is that as soon as you open any of the windows/doors, the AC automatically turns off. A message on the thermostat then alerts you that it will come back on once you close the windows. I haven't yet figured out how this particular hotel room is sensing that things are open, but it's relatively easy to do this at home through smart thermostats and sensors like these . I make a real concerted effort to do this manually, and so it's great to see it automated in a hotel room, where people are naturally going to care less about wastage. Europe is so far ahead of North America when it comes to energy efficiency.