LEDs in different colors show four levels; empty, 1/4, 1/2 and 3/4 full. 3 sensors mounted (glued) with a 3M tape on the outside of your tank. Very easy to retrofit on both new and older tanks. No drilling or disassembly of the tank is required. Measures from the outside, never risk of leakage. Everything included: 1 LED panel (display), 1 controller, 3 sensors (1 m cable), 1 DC cable (1.8 m) and 1 panel cable (1.5 m), 1 3M surface cleaner, 1 extra sensor 3M VHB tape, 1 velcro strap (control unit) and instructions in English. No battery is included in the package. We recommend a minimum current of 500 mA. For all these tank materials: Stainless steel max 3 mm Steel max 3 mm Aluminum max 5 mm Polyethylene max 12 mm Fiberglass max 8 mm Details: Volts: 12-24 V