What do I have to do at a checkpoint ?
Checkpoints are strange, and complicated, legal exceptions to the Constitutional right to be free of unwarranted searches and seizures. Checkpoints allow officers to stop you, i.e. seizure, without any suspicion that you are doing something wrong.
This would typically be unconstitutional, but the US Supreme Court [see City of Indianapolis v. Edmond, 531 U.S. 32 (2000)], and t