Nest and Ecobee can work with many common 24V heating and cooling systems, including some heat pumps

https://veloriftlabs.com/s/IodvcBR5NC3xzr9S8vk-5

Nest and Ecobee can work with many common 24V heating and cooling systems, including some heat pumps, though certain homes may need a C-wire or add-on power accessory.