No need for a sensor in every room. The system uses the motion sensors for occupation, takes an average of all the sensors, and then adjusts the temp accordingly; with one room being the warmer than the others, the one occupied, and leaving other rooms cooler. No system is going to keep every room at the set temperature so there is no need to purchase multiple sensors. Just place one sensor in the most occupied room of the house, single story home mind you, and set your temperature. Mine works fine with just one extra sensor and the built in sensor of the thermostat. Save your money for other smart home items and no need to purchase extra sensors. The only reason for extra sensors is if you spend more time in multiple rooms, the sensors have a motion sensor to determine if you are in the room, this may cause other rooms to seem warmer or cooler than you would prefer them to be but the room you are occupying will be just right. Your system might differ from mine but this has been my experience for the last two months after installation. Mine came with the thermostat and an extra sensor so I placed the extra sensor in the room used most often and have had no issues.