Neptune Optical Sensor
This sensor plugs into your FMM and, using reflected infrared light, will signal your Apex when it changes state from being wet to dry or dry to wet. This sensor can be used for constructing your own ATO (auto-top-off), as a high-level warning sensor in your sump, water storage level sensor, and much more. Included are a fastening nut and silicone washer. These sensors are sold individually.
Also available with an Optical Sensor Magnetic Mount.