Traditional thermostats only require power through the four classic wires while smart thermostats typically require low- voltage power all day in order to run the display screen and some basic functions. Once you've wired and installed your smart thermostat, you can connect it to other devices in your home via Wi-Fi or occasionally Z-Wave. While they’re compatible with many systems, I would still take a moment to check and make sure that a thermostat works specifically with the smart home setup you use at home.