Put it in your high-traffic, hot and cold spots.
Minimizing the hot and cool spots is the main function of the room sensor. Place the sensor in your busiest rooms, or where you feel are usually warmer or cooler than the rest of your home.
For the best occupancy detection, place the sensor about 5 feet off the ground and facing the entire room. Avoid placing it near vents, fans, windows, direct sunlight, and other heat/cold sources as this may influence the sensor's readings.