A machine that "works but breaks often" does not work, period. And if it "breaks often", I suspect that the problem is a fundamental one that won't be solved by a "tweak".[/QUOTE]

I would disagree that they don't work. I work in the nuke power industry and I have seen them work up close and personal. I have seen the puffers detect shot gun shells in someone's coat pocket. I have also seen security testing the machines after some of my guys calibrated them and they did detect the contraband materials. Now on a large scale, there may be issues, but they do work with several thousand people a day going through them. You will not enter the protected area of any US nuke plant without going through a puffer of some kind.