There are several thermostats on the market today, including Nest and Ecobee. Most of them have only a single sensor mounted inside the thermostat. The problem with that approach is that it only accounts for the current temperature in the specific region where the thermostat is mounted. Ecobee makes a thermostat that comes with an extra sensor, which is also mounted inside the house. Once it collects the data from both sensors that are inside, it averages them up and uses the average temperature to control the HVAC system. We went with a differential approach with one thermostat mounted outside the house. Theoretically, accounting for the outside temperature will make the thermostat more efficient by always running the HVAC system inside its maximum efficiency zone.