Yeah, I looked into it a while ago and there is like a yellow line that provides constant power to the thermostat. If you don't have it, then they make them with batteries, but you have to keep replacing them all the time. Not a huge deal, but if they happen to go out on you while you are away on a trip and you want to crank the heat or A/C for when you get home, it's not going to work. Definitely a first world problem in the grand scheme of things!