One of the toughest challenges of indoor gardening is determining when a plant needs water, even if you can see the top of the soil, or you can poke a finger into the pot. Hurray for Moisture Sensor, a probe that you nestle into your pot and leave. As the soil dries, the sensor will flash red. The drier the soil becomes, the longer it will flash. A brief flash? Water that fern! Red light special flashing? Time to water plants that prefer to live on the drier side, such as succulents, peperomias, and sansevieras. Take the guess work out of watering. Metal probe is 5" long, total length of sensor is 8".