One of the most efficient smart thermostats is the Nest thermostat. This is one of the best ways to keep your house cool while you are away. This thermostat keeps a record of the temperatures in your home. You don't have to do anything. All you have to do is turn the thermostat to the desired temperature. The thermostat will automatically adjust the heat or air conditioning to meet the desired temperature. The Nest thermostat is the best choice. It's easy to use and it's affordable.