Preaction systems are designed to protect water-sensitive areas such as freezers, museums, computer rooms, and clean rooms. These locations contain water-sensitive equipment, precious objects, or sensitive areas where accidental water discharge is undesirable. Preaction systems may take the place of dry systems. 
Preaction systems utilize closed sprinklers, and compressed nitrogen or air in pipes, to increase the pressure more than water below the clapper of the valve. Preaction systems require a detection and release system. When activated by a detector, the valve will open, and allowing water to flow into the system pipe. When the heat source activates a sprinkler, water flows through only the open sprinklers.