The Indoor/Outdoor Temperature and Humidity Sensor by HAI Includes all of the features of the 31A00-1, and adds an electronic humidity sensor, reporting 0 to 100 percent relative humidity. Use as a Humidistat: High and low limits can be set for taking action (i.e. turning on the bathroom vent fan, running a/c in de-humidification mode, turning on humidifier in heating mode, etc.). or reporting high or low humidity conditions in homes, greenhouses, wine coolers, humidors, etc. This sensor uses two zones; one for temperature and one for humidity.