History

• The Fourth Amendment of the U.S. Constitution, ratified in 1791, protects each citizen's property and person from unwarranted searches. When attempting to obtain search authorization from a judge, an officer does not have to prove the person in question committed a crime, but rather needs to show probable cause that the suspect committed a crime or that evidence of a crime exists at a specified location.
  
  

Function

• The need for a written warrant protects citizens from unreasonable search and seizure. Law enforcement officers must give sworn statements to a judge, describing in detail what and where they intend to search. Officers, when executing a search, must present the written warrant for the search to be legitimate and lawful.
  
  

Exceptions

• In the U.S., a warrant isn't always needed. The most common instance occurs when a civilian gives an officer consent to search his person or belongings. If evidence of illegal materials or criminal activity sits in plain sight, the officer can carry out a search. At an airport or at a border, agents may search a person without a warrant. Also, in an emergency situation, officers can forgo obtaining a warrant while handling an immediate threat.
  
  

Significance

• In the United States, an illegal search or lack of a legitimate warrant can lead to dismissal of a court case. Throughout U.S. history, much discussion has ensued over what constitutes a lawful search. The USA Patriot Act of 2001 stirred further debate over warrants and Fourth Amendment rights.