Millions of travelers never have trouble, but thieves are out there -- especially in international airports. Watch out for "shoulder surfers" -- one crook pretends to videotape friends while zooming in over your shoulder to steal your mobile phone or credit-card numbers. Another trick: One thief stalls the metal-detector line with keys, change and other metallic objects, distracting everyone while an accomplice steals carry-ons from the other end of the conveyor belt.