SmarterSpa SMARTERSPA Portable Spa Salt Chlorinator with Sensor 110/220V is a saltwater system uniquely designed for hot tubs and spas. Turn your hot tub water into saltwater by adding salt (about a teaspoon per gallon), and then let our chlorine generator take care of your sanitation needs day after day. The SmaterSpa comes with a sensor. It's the only saltwater chlorine generator with chlorine control built into the cell. SmarterSpa knows when to turn on, and when it does it will be on for a fixed amount of time. When it turns off, it will be off until it needs to turn on again based on the chlorine measurement. Eliminate the guesswork or the need to properly set the power level. Vacation mode and temperature compensation are not needed as control is based on the chlorine level.