Visual-Only Features Compare these features with other manufacturer's products !

Failsafe feature allows an operational self check everytime you open the door. U.S. & Foreign Patented Ball-In-Tube Technology… Indicates the actual directional airflow, as opposed to an absolute differential pressure reading! Simple, Visual, Accurate and Reliable ! Visual SELF-CHECK performs each time the door is opened !!! Installs in minutes . . . No electricity or linkages are required! Requires a minimum of 0.01" w.c. for fail-safe feature Lifetime Warranty!  Great item to function as either a stand-alone or as a safety check for existing monitors ! Click here to see VISUAL ONLY monitors!