At my favourite mini-hotel in Saigon, the pretty receptionist smiles as you leave the hotel - and then goes over to the fuse box and pulls your fuse out! (Fridge and power points still work. Also these are backed up by the generator during power cuts.)

When you return, after you've passed reception, she puts it back in.

Thing is - they have really powerful individual aircons. In the time it takes me to get to the room, the temperature is already down from perhaps 33-35 to below 30. Within 20 minutes it's below 25. I've got it as low as 17 - quite an achievement for Saigon (though the cleaners won't go near it in those freezing conditions).

I don't understand all the earlier comments about aircons taking "hours" to get the temperature down. They must be seriously undermaintained or underspecified.

In my usual hotel in Taipei, only the TV and aircon are controlled by the key card. When you leave the room, the aircon goes to 25 (unless you set it higher). On return it resumes full power. Only takes 10 or 20 minutes to get to 20. I'm quite happy with this arrangement.