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

https://damienresk232.quantlynix.com/posts/what-to-know-before-replacing-an-ac-system-in-salt-lake-city-2

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.