Visiting the White House is not unlike preparing to board a plane. Bags pass through x-ray machines and visitors through metal detectors. The White House, though, benefits from some augmentation: specifically, so-called backscatter x-ray technology, in which devices capture the radiation bounced back from objects. It can generate more detailed images than conventional x-ray machines and can even call out organic materials, such as liquid explosives.

Such technological fixes have rapidly come to the fore in the wake of recent terrorist revelations--and not for the first time: backscatter was widely touted as a solution to hijackings and other air travel incidents as long ago as the 1980s. Other high-tech solutions--millimeter-wave sensors for personal screening, quadrupole resonance to detect things like bombs in shoes, neutron-bombarding devices to precisely establish the chemical makeup of objects, as well as a host of others--can detect an array of threats, for a price. Already the Transportation Security Administration (TSA) has installed at least 100 trace detectors, designed to pick up minute quantities of various suspect compounds on clothing, luggage or people, at major airports throughout the country. But ultimately, technology can never provide the perfect security answer.