Visi-Therm Stealth Submersible Heaters combine an advanced, streamlined design with water-calibrated accuracy for superior performance. These UL listed, shatterproof heaters will actually shut off when the water level gets too low and will turn themselves back on when the water is back to an acceptable level. Features a temperature select dial on the top that contains an LED that glows red when it is heating and green when the temperature is OK. The heater contains a reliable solid state circuitry accurate to +/- 1F. An internal mesh heating element with mica core, coupled with epoxy fill ensures the most efficient heat transfer and elimination of the rattling coils. These reliable, safe and accurate heaters come with a manufacturer's lifetime warranty.