New and exciting level indicator. Install, make settings and see the results on your smartphone. Free app for iPhone and Android phones is available for free download. You can use Gobius Pro for all liquids and tank materials. 12-24 volts. Choose water, fuel, waste or other liquids. You can have a maximum of 9 sensors/tank. Measurement from the outside of the tank, nothing on the inside. Bluetooth and app for your phone included. Works with the following tank materials: Stainless steel, max 3 mm Steel, max 3 mm Aluminium, max 5 mm Polyethylene, max 12 mm Fiberglass, max 8 mm The sensor(s) are attached to the side of the tank with the included 3M attachment pad. 2 pcs included. Alarms when the level in the tank reaches above or below the sensor. Can choose over or under in the app. For more information see https://www.gobiuspro.com/ or download the Gobius Pro app which contains a guide and link to a tank calculator.