This 4 inch reduced pressure zone assembly backflow preventer help stop the reverse flow of liquids due to backpressure or backsiphonage, where potential health hazard exists. This extremely compact and lighter than a traditional designed assembly is approved for horizontal installation as long as the backflow assembly is installed in accordance with the direction of the flow arrow. This assembly consists of a stainless steel body with a quick access sleeve, torsion spring check valves, grooved gear operated butterfly valves with tamper switch, test cocks, and a corrosive resistant stainless steel bottom mounted pressure relief valve. This backflow assembly contains a flood sensor with SentryPlus Alert(R) technology to detect excessive water discharges from the relief valve. When activated through an add-on sensor connection kit, the flood sensor relays a signal that triggers notification of potential flooding to service personnel. The add-on sensor connection kit is available for building management systems and cellular communication.