> My biggest worry in hotel rooms these days is how to rig the A/C to stay on while I'm out.

Heated blanket on the thermostat? Or do they have timed-shutoffs or door-key based systems that cuts off the electricity when you leave? What do you do then?

Most of them just have a slot for your room key to turn on the electricity and/or A/C, but many times it is a physical which i.e. it doesn't care what gets stuffed into the hole and often there is some kind of brochure that can be folded/ripped into card shape to trip the switch.

Ask for a second key and leave it in the slot?

Those slots don't require a specific key. Put your library card in there and it'll work fine.

They get suspicious when I pay for X occupancy but request X+Y keys.

Hotels routinely give me two cards when I check in--and certainly will if I ask. I usually stick one in my wallet and one in my bag or whatever so I'm less likely to accidentally leave the card in the room.

Usually you can stick anything that has the correct form into that slot. Even thin cardboard :)

Charging devices, leaving the TV on to fake occupancy as the article suggests.

Also AC is much more efficient if it keeps the room at a stable temperature rather than letting it heat up and then cooling it down again. I never set it that low myself but some hotels don't have a temp setting, that's true

AC might be comparatively more efficient at cooling the room 1 degree rather than 5, that doesn't mean that keeping that temperature for 8 hours will consume less energy than cooling it once you come back in.

If it were really overall more efficient it would be cheaper for the hotel owner to just keep it on all the time, but clearly it's not.

It really varies. Some places have the bare minimum of air conditioning to say they have it, but underbuild the system such that there’s no chance of recovering if you get back during the day while it’s still sunny&hot outside.