ATO One is a smart water replenishing device that requires only the sensor and the refill pump to be installed. It can be used after power-on without setting any parameters. The optical level sensor is used to monitor the water level to determine whether water needs to be replenished. The float level sensor is used to prevent overflow. An optional float level sensor is available to monitor the freshwater reservoir for water shortage. ATO One is rich in status indicators. When the Anti-overflow Sensor or overtime, the refill pump is not inserted or the freshwater reservoir is short of water, the ATO One will have an indicator light and a buzzer alarm.