Well, traveling domestically isn’t the issue. It is going over international borders where customs comes into play. If you’re coming into the USA right now and you’re a citizen (and probably if you’re a green card holder), the general thinking is that they can’t stop you from entering the country, not indefinitely. They can hold you for questioning (and it is open ended how long they can get away with) but have no right to deny entry. If you refuse to unlock* a phone, they can confiscate it for “analysis” or whatnot and you may or may not see it (or trust it) ever again. Same with laptops. That said they can use your finger against your will to fingerprint unlock your phone (per a court decision until it is reversed) so stick to pin codes.
I am not a lawyer.
