With two smart thermostats in a home that has multiple zones (e.g., upstairs and downstairs systems)., you’re saving 1,500–1,800 lbs CO₂ per year (0.75–0.9 tons)

According to EPA and ENERGY STAR, a single smart thermostat can save ~8–10% on heating and cooling energy.
For the average U.S. home, that’s about 500–900 kWh/year or 50–90 therms of natural gas saved.
That translates to roughly 750–900 lbs of CO₂ per thermostat per year, depending on your fuel source.

Eat what you buy – Wasted food = wasted energy, water, and money.
Kill the vampire loads – Unplug stuff that’s not in use (chargers, printers, etc.).
Combine errands – Fewer trips = less fuel burned.