Liquid Crystal Aquarium Thermometer that mounts to the outside of your aquarium. It is Accurate, Easy to Read, Safe – Non Toxic, Unbreakable, Non-corrosive and can be Repositioned. Simply stick to the outer wall of the tank. The best thing about these thermometers is that they keep the temp in sight and in mind. If the heater or chiller in your tank were to have an issue you would know about it.