What could happen if you refuse to unlock your phone at the US border?

"One of House’s lawyers, Catherine Crump, who was then an attorney at the American Civil Liberties Union and now teaches law at the University of California, Berkeley, told Ars that the government claimed House had committed a misdemeanor in violation of 19 US Code Section 507. "They claimed he violated a statute requiring people to provide aid to border officials upon request," she e-mailed. "I am not sure how much of this was government posturing. Presumably a lot—I have never heard of anyone being charged under this statute for not disclosing a password. The answer to how long someone could be detained is likewise unclear. Other countries have limits on how long a citizen can be held at the border, but there is no such publicly declared limit in the US. This is all symptomatic of a more general problem. There are not clear limits on what border agents can and cannot do, and civil liberties suffer as a result.""