Gobius Pro 1 External Fluid Level SensorInstall, make settings, and see the results on your smartphone. Free App for iPhone and Android phones included. You can use Gobius Pro for all liquids and tank materials. 12 – 24 Volts. Choose water, fuel, waste, or other fluids. You can have max 9 sensors/tank. Features:Measuring from the outside of the tank, nothing on the insideBluetooth and App for your phone includedWorks with the following tank materials:Stainless steel, max 3 mmSteel, max 3 mmAluminum, max 5 mmPolyethelene,  max 12 mmFiber Glass, max 8 mm