Originally Posted by
chollie
If you're an American citizen without outstanding warrants, they can't detain you indefinitely, although they can hold you for hours (how many is unknown) without restricted access to food, water and toilets.
They can, however, 'detain' your electronic devices for further investigation -
They can only do that with reasonable suspicion supported by articulable facts, at least in the Ninth Circuit. I've had them threaten to seize my phone and laptop twice, and both times they took my devices out of the bags and said "We're seizing these."
They were bluffing both times, it's a tactic they use to get people to answer questions/reveal passwords.