The 4th Amendment protects people from unlawful searches and seizures.
The right of the people to be secure in their persons, houses, papers and affects, against unreasonable searches and seizures, shall not be violated, and no warrants shall issue, but upon probable cause, supported by oath or affirmation and particularly describing the place to be searched, and the persons or things to be seized.
In a nutshell, this means the police are not allowed to search you or your house without a warrant or probable cause.
The 4th Amendment was added to the Constitution due to actions by British tax collectors prior to the American Revolution. The British used general warrants to enter and search any house they chose without the need of evidence to validate possible wrongdoing. This was a major reason the Founding Fathers added the amendment, in order to protect Americans from this variety of privacy invasion by the federal government.
A ‘search’ is defined as when a public official (i.e. police officer), seeks out documents or items considered to be ‘private’. ‘Seizure’ is when an individual is not free to leave, such as being placed under arrest. If an item is seized, the individual is unable to retain possession of it – such as a vehicle or wallet.
In order for a public official to conduct “search and seizure”, s/he must first obtain a warrant - a legal document written and signed by a judge. Acquiring a warrant involves the official requesting the document to provide evidence to the judge, demonstrating why the warrant is necessary.
The 4th Amendment also requires the existence of “probable cause” (evidence indicating a crime was most likely committed). This has to be provable prior to the search and/or arrest taking place. Evidence alone, however, does not automatically indicate the existence of probable cause.
There are also times when certain places/situations result in people being stopped or searched without a warrant. An airport is a perfect example. Nowadays, when you purchase an airline ticket, you automatically surrender a portion of your 4th Amendment rights. The same applies with public roads. For example, a roadblock on the highway in search of fugitives or illicit drugs can possibly involve the search of your car without a warrant.
Today the Fourth Amendment is also considered to be an enormous gray area legally as the courts investigate how this right applies to today’s new and emerging technologies such as electronic communications and cryptography (the art of writing or solving codes).
“Now, one of the most essential branches of English liberty is the freedom of one’s house. A man’s house is his castle; and whilst he is quiet, he is as well guarded as a prince in his castle.”