Outside of legal circles, most people don't realize that your Fourth Amendment right to not be subjected to "unreasonable search" is suspended at the borders. Ghappour explained this gives border agents a lot of leeway in terms of how much they search and detain people crossing into the US. He talked to Ars about recent cases where people have been asked to hand over the passwords to their phones and computers, as well as other personal items. During the discussion above, we also touch upon surveillance at the border and what's likely to come next in terms of sensors, drones, and data mining for "national security threats."
from Ars Technica Live: What to do when border officials ask for your passwords