FEBCO Series 850 Small double check valve assembly backflow preventers includes a freeze sensor for use with SentryPlus Alert® technology to monitor temperature nearing the freezing point. Activated by an add-on connection kit, the sensor triggers alerts to help facility personnel reduce equipment damage and repair that may result from cold weather conditions. Available for building and irrigation management systems. This series is designed for non-health hazard applications, to protect drinking water supplies from dangerous cross-connections in accordance with national plumbing codes and water authority requirements for non-potable service applications such as irrigation, fire line, or industrial processing. Standard assembly with ball valves or union end ball valves.