If you use the Honeywell Weather Station to see all local weather conditions at a glance, you can expand your temperature and humidity data by adding the Honeywell Weather Station Extra Sensor. This thermo-hygrometer measures temperature and humidity up to 328 feet away from the weather station, and it's safe for indoor or outdoor use. The Honeywell Weather Station Extra Sensor is powered by two AA batteries (sold separately). With five distinct channels, up to five different thermo-hygrometers can connect to your Honeywell Weather Station, so you'll be able to keep an eye on the temperature and humidity outside as well as in different areas of the house, such as the attic and wine cellar.