Power monitor light: red for heating and green when aquarium has reached set temperature. Fully submersible and can be placed horizontally or vertically in the aquarium. For freshwater and marine aquariums. Shatterproof and nearly indestructable with durable aluminum core and no glass components. Automatically turns off if heater is left out of water, resets and works normally when placed back in the water. Large temperature control knob makes modifying the temperature easy.