New security technology could make it more difficult for terrorists to pull off attacks like the ones that happened this morning in Brussels.
A system under development, called a "Tunnel of Truth," goes beyond the current scanners that image passengers or luggage before they board an airplane and screens people as they enter an airport and subway station.
"What happened in Brussels is a really tough problem," said Cameron Ritchie, vice president for technology and product development at Morpho Detection, a international biometric and security firm.
"We operate at checkpoints or with luggage before it goes on a plane. In both cases, you have an orderly queue that makes the job a whole lot easier. The issue is that today these guys didn't present themselves to be inspected."
But the Department of Homeland Security is funding research into a "Tunnel of Truth," a long walkway flanked by several scanning devices that can passively detect explosives, weapons or other contraband without creating a passenger bottleneck.
Video cameras would also record passengers' facial expressions for signs of nervousness, erratic behavior or other "tells" that indicate they might be hiding something or lying about their identity.
Morpho is already working on the first step in this tunnel, a sensor that can remotely "swab" the air around a passenger's body for chemical traces.
"That's the holy grail for our field," Ritchie said.
Morpho and other firms have designed and built an increasingly sophisticated array of devices to stop trouble: CAT scanners that check for high-density materials that could indicate an explosive device, X-ray diffraction machines that scan each bag for chemicals that resemble explosives, detectors that analyze swabs of travelers skin to check for minute traces of explosives.