The HYDROS Rope Leak Sensor is a flexible rope-like material that detects the presence of moisture anywhere along the rope. It can sense when freshwater or saltwater is underneath it and use that information to protect your aquarium, home, or office from serious damage. The rope leak sensor plugs directly into any available Sense Port on the Control XS, Control X2, Control X3, Control X4, Control X10, or any future HYDROS Control device.