In the months after the Sept. 11, 2001, terrorist attacks, government officials and industry leaders talked excitedly about how they expected technology to plug many of the gaps in airport security.

They envisioned machines that would quickly detect explosives hidden in luggage, spot plastic explosives or other weapons through people's clothing, identify a flicker in the eye of a suspicious character.

But six years later, little has changed at airport checkpoints. Screeners still use X-ray machines to scan carry-on bags, and passengers still pass through magnetometers that cannot detect plastic or liquid explosives. The Transportation Security Administration has yet to deploy a machine that can efficiently detect liquid bombs, forcing millions of air passengers to check bags or pare down their toiletries to three-ounce containers in carry-on baggies.