Aqueon Submersible Aquarium Heaters are made from thermal shatter-resistant quartz glass and were designed to absorb impacts making them extremely durable. A power indicator light turns on when the unit is heating. UL approved the heater is also programmed to turn itself off when not properly submersed to avoid overheating and damage. Can be positioned at a vertical or horizontal angle. Can be used in fresh or saltwater fish tanks. 6-Foot power cord.