Take the guesswork out of when to water with smart moisture sensors. Take the guesswork out of when to water with smart moisture sensors. From houseplants to gardens to lawns, Gro™ Water Sensors measure the moisture content in your plant’s soil and uses science to tell you when they’re thirsty. Getting your smart water sensor up and running is as easy as plugging in the hub, placing the sensor, and connecting them with the Gro™ Connect app.