Just FYI...because their wording is confusing: You can use this system for high level or low-level monitor / shut off without a controller. Put it in your skimmer cup to shut off before it overflows. Or, put it at the rim of your tank in case the water level starts rising. Or, put it in your sump in case water goes below it and you need to shut off the return pump. It's great for redundancy. I have two of them and don't need this one.