No need for a warrant in the international zone at O'Hare airport.
Americans are protected from warrantless search in America — but not at the nation's borders. The imaginary line separating the United States from the rest of the world has become a critical demarcation for the privacy of the country's citizens, as new documents from the ACLU and the ongoing Snowden leaks make clear.
David House worked as a fundraiser for the defense of Chelsea Manning in her court-martial for uploading classified information to Wikileaks. That brought him to the attention of the government, perhaps predictably; he was questioned by authorities about his relationship to the Army private. What he didn't know, though, is that he'd been flagged in the Department of Homeland Security's TECS system. (TECS is not an acronym for anything.) That flag, according to documents obtained by the ACLU, looked like this.
From a DHS report
DHS letter to the Army CIC
The Associated Press reports that House, who relied on that Asus PC for his work, had no sign that the seizure was coming. During the questioning several months prior, the government made no suggestion that it sought the contents of his hard drive. Were it to want to search the device at that point, of course, it would need a warrant. Once House arrived in the international zone at O'Hare, however, that need was obviated.