Had new furnace and AC installed in 2022 - stipulated I didn't want a "smart" thermostat. Installer brought out a dumb digital unit - said it was more sensitive than the old mercury switch unit it replaced. However he put my old thermostat in the new unit's box, returned it to me and said to hang onto it - said the mechanical tech it uses is almost foolproof and "You never know what they have in mind". He knew.