The MagnaFlow 387-01-5190-35 SKL-WP2 Spot Check 1 Gallon Container is a portable spot check device that can be used to test for the presence of air leaks in residential and commercial HVAC systems. The device uses a patented magnetic flow technology to detect air leaks in ducts, registers, and other areas. The MagnaFlow 387-01-5190-35 SKL-WP2 Spot Check 1 Gallon Container is easy to use and can be carried in the trunk of a car for quick and easy use.