Not long ago some Israeli security hard cases explained how they handle this issue at Ben Gurion. You can probably still find it online somewhere, basically their monitors are highly trained in profiling and they use psychology and hyper profiling to spot potential threats.
I've heard bits and pieces about the Israeli methodology, and I've also heard critiques of its potential for application in the US (mostly, centering on the idea that our population is too big, too diverse, and too spread out to accommodate the training and consistency of the Israeli program).
Whatever the case, one thing does seem fairly clear: that the Israeli investment in people, rather than machines, seems to be paying a good dividend. And I'm tempted to say that we'd be better off staffing airports with better people and slightly older / less intrusive machines, rather than cutting-edge machines and bottom-of-the-barrel staff.
I want to say it works like a bomb but...