http://en.wikipedia.org/wiki/Fourth_Amendment_to_the_United_States_Constitution
4th Amendment of the US Constitution
Arrest
When a person is arrested and taken into police custody, they have been seized (e.g., a reasonable person who is handcuffed and placed in the back of a police car would not think they were free to leave). A person subjected to a routine traffic stop on the other hand, has been seized, but is not "arrested" because traffic stops are a relatively brief encounter and are more analogous to a Terry stop than to a formal arrest.[39] A police officer does not have the authority to arrest someone for refusing to identify himself when he is not suspected of committing a crime, unless state law says otherwise.[40] A search incidental to an arrest that is not permissible under state law does not violate the Fourth Amendment, if the arresting officer has probable cause.[41][42]
In Maryland v. King (2013), the Supreme Court upheld the constitutionality of police to swab for DNA upon arrests for serious crimes, along the same mentality that allows police to take fingerprints or photographs of those they arrest and detain.[