This Moisture Sensor can be used to detect the moisture of soil or your pet plant's water level, let the plants in your garden reach out for human help. With the Octopus Electronic Bricks interface can very easy to used with the sensor shield V4.0.

    

This sensor uses the two probes to pass current through the soil, and then it reads that resistance to get the moisture level. More water makes the soil conduct electricity more easily (less resistance), while dry soil conducts electricity poorly (more resistance).