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) with restricted access to food, water and toilets and no access to a phone.

They can, however, 'detain' your electronic devices for further investigation - and they can confiscate anything that appears relatively new, could have been purchased overseas, and that you do not have a receipt for.