The Rena Smart heater has anelectronic sensor that accuratley monitors the temperature which can be set from 20-34 degrees Celcius. The heater incorporates a warning light to alert the fish keeper to any undesired temperature change. The light will flash fast if the temperature is +3 above and when the temperature is -3 below. A huge benefit of the Smart Heater is that it is unbreakable. Made of composite materials, the Smart Heater is insensitive to mechanical or thermal shocks. Safe to handle, the product also incorporates a safety feature that swtiches off the device when it is not totally submerged in water. The heater has a unique design that is not only unobtrusive, but also allows it to be connected to the inlet tube of the Rena XP range of external filters as well as many other externals. Temperature Warning Light Unbreakable Highly Accurate Attractive Discreet Design Safe to Touch Auto Safety Off Function