So, umm, turning your phone off won't matter much if the border agent tells you to turn your phone on, log into your social media, and show your posting history otherwise you can't enter.<p>> If you refuse to unlock your phone when asked, authorities can seize it and will most likely need to obtain a warrant to open it, he added. However, visitors can be denied entry to the United States for refusing to unlock their phone.<p>As I understand it, they know the Facebook, Instagram, LinkedIn, Pinterest, Reddit, Tumblr, Twitter, etc. usernames for most foreigners because that's required as part of the visa process.<p>If the border agent wants you to log into an account they know you have, under threat of being denied entry, will you say no?