Aprilaire Model 56 automatic humidistat designed for low voltage (24v) humidifier control. Computer-equipped, completely automated, never needs manual adjustments. The advanced computer technology measures the outdoor temperature and indoor humidity and continually adjusts your homes indoor humidity to its optimum level. The outdoor temperature sensor is located outside and is connected to the humidistat with regular 2-conductor thermostat wire.

• humidistat 
• outdoor temperature sensor with 36-inch wire and bracket 
• manual mode resistor