The burden of proof for being charged is just probable cause, which is quite low. You wouldn't be held very long- unless you're deemed a flight risk by a judge,

The burden of proof for being charged is just probable cause, which is quite low. You wouldn't be held very long- unless you're deemed a flight risk by a judge, you'd be let out on bail. I think the risk is low for a random person, but if you're Julian Assange or someone equally interesting to the feds, and are known to use relatively sophisticated cryptography all the time, and an image of a phone taken at the border turns up evidence of a large encrypted partition that you denied existence of, I wouldn't put it past a prosecutor to put it to a grand jury and come out with an indictment.