Manufacturer and Direct Sales of the patented BALL-IN-THE WALL® BALL-IN-TUBE (™) DOME-ON-THE-WALL(™) Room Pressure Monitor with Integral Failsafe Check Feature. SIMPLE, RELIABLE, NO ELECTRICITY REQUIRED. U.L. Fire-Rated Wall Kits available. In addition to our patented indicator we stock, look for our re-introduction of our dependable alarm units and new models soon to be available in the Summer of 2020