The Smart Moisture Sensor is a gravity fed watering system that has 4 independent watering programs. These programs can be selected by simply turning the dial to water a maximum of 20 plants for a maximum duration of 40 days. LED light located on the programming panel indicates when unit is in use or when battery is low. Isolated tank prevents condensation and non-slip rubber feet avoid scratching of surface or sliding of tank. Operates on one 9v battery (not included).