A new program is in effect at 4 U.S. airports-- screening of passengers' documents:

A new device that scans documents for traces of explosives has made its debut at four of the nation's busiest airports, where officials will use it to screen selected passengers. Federal security screeners started testing the equipment Wednesday at O'Hare International Airport in Chicago. It is also being used at Los Angeles International Airport, John F. Kennedy International Airport in New York and Washington Reagan National Airport to detect chemical residue on the surface of items such as wallets, passports and airline boarding passes.

Of course, the screening isn't being done on all passengers.

It will be used for passengers selected by security workers and those who set off alarms at checkpoints.

There may be lots of false positives:

Dozens of chemicals could trigger the scanners, including nitroglycerin taken by heart patients, fertilizer and gunpowder residue.

After a 30 day trial period, the Government will decide whether to extend the program to all airports.