If you cross in to or out of the US, the government might seize your electronic devices—whether it's got a warrant or not. David House, a fundraiser for Chelsea Manning's legal defense fund, found that out the hard way in November 2010, after a trip to Mexico. He sued the Department of Homeland Security, and as part of the settlement, obtained documents outlining what, until now, has been a mostly secretive technique, the New York Times reports. “I think it’s important for people who consider themselves politically inclined to know what dangers they now face in a country where they have no real guarantee of privacy at the border," says House.
Homeland Security can put a "lookout" alert on anyone it wants in the computer system that screens international travelers. When that person books a flight, Homeland Security is notified, and dispatches agents to meet the traveler. In House's case, they seized his data and sent it to Army Criminal Investigation Command, all without a warrant. Critics say the process violates citizens' Fourth Amendment rights, but courts have generally supported it as an exception because it's a useful tool against drug smugglers, child pornographers, and other criminals.