On May 15, Amsterdam's Schiphol airport began using new body-scanning machines at security checkpoints, the first major airport to use the technology to find metals and explosives hidden under clothing.

The "security scan" system, which uses harmless radio waves to display head-to-toe images of people, is also being used by other airports on a trial basis, but Schiphol is the only one to deploy the technology for regular use at its checkpoints.

Going through the scanner takes about three seconds, allowing users to avoid metal detectors or body searches. For privacy, the digital images are viewed by security personnel in another room and deleted after they are viewed.

Schiphol handles about 160,000 passengers per day at peak times and is Europe's fourth-busiest hub. So far the security scan is voluntary but officials are hoping to expand it to include all passengers, crew and personnel.

Schiphol is one of the world's most modern airports, with flat-panel screens, airport-wide Web access, and iris-scanners already on offer to those who want to bypass passport lines.

Some people object to using the machines because they are concerned about the radio waves, rather than privacy, said Schiphol's Chief Operations Officer Ad Rutten.

But the alternative, being hand-frisked, is "never a happy story," Rutten says.