(IANAL) If you're a US citizen, indefinite detainment without cause is unconstitutional: they must release you eventually; you also (provided you have your pass

(IANAL) If you're a US citizen, indefinite detainment without cause is unconstitutional: they must release you eventually; you also (provided you have your passport/can prove citizenship) have a right to enter your country. Further, if they try to detain you indefinitely illegally, you have the right to a writ of habeas corpus — a legal challenge that your detainment or jailing is illegal (your jailor must go before the court and show cause that he/she has the right to hold you). (Though, if you are in this position, you may need someone to file it on your behalf.) Again, I'm only asserting this in the specific situation of a US citizen attempting to enter the US. My understanding is that they are permitted to search you, for the narrow purpose of border security. (I.e., the search here is not a violation of fourth amendment rights.) But I don't see how they can force you to divulge your password. You might not get the phone back, though, and they'd likely make your life very difficult; it's probably better to not mess around with them, and plan ahead. Specifically, I don't think leaving and trying again is ever an option, and wouldn't look good to the officer.