This is a steam (water) sensor from DFRobot. This steam sensor can be connected to the Arduino IO Expansion shield directly. The output voltage will increase when the humidity of the sensor surface goes up.
Notice: The new version of analog sensor port pin mapping has been changed as the following two features.
Warning: The connector is not waterproof, please be careful not to put the connector directly in water.
Steam sensor x 1
Analog Sensor Cable x 1