Fourth Amendment

On the surface the Fourth Amendment to the United States Constitution seems pretty clear, but when it comes down to it, it can be quite complicated. The text is pretty short:

The right of the people to be secure in their persons, houses, papers, and effects, 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.

Basically if the police are investigating a person they have to obtain a document from a judge that allows them to burst into that person's private property and search through it for evidence (this generally includes wiretaps). Likewise if the police want to arrest you they have to get permission first. In order to obtain this document the investigators have to convince a judge that there is "probable cause" that a crime has been committed or that evidence of said crime exists. If somebody is arrested and put on trial on the basis of evidence illegally obtained such evidence must be excluded from the trial.

Ifs ands or buts
Police and criminal procedure is rarely as cut and dry as the Bill of Rights would seem to suggest; there are many exceptions to the need for warrants. These include:


 * If the officer actually sees you committing a crime he or she may arrest you.
 * If you left evidence somewhere outside of your property (including the trash).
 * If you invited the officers in and let them look around.
 * Possible life or death situations (commonly known as "exigent circumstances"), e.g. officers witnessing gunshots emanating from a building can enter without a search warrant.
 * If you are in the custody of the U.S. Prison Service, the fact that you are in custody is reasonable enough for any search and seizure applied against you.
 * If you are a government employee in certain fields, you may be subject to "suspicion-less" random drug testing.
 * If you are a public school student involved in competitive extracurricular activities, you may be subject to "suspicion-less" random drug testing.

The case law on what does, and doesn't, qualify as "probable cause" could fill several volumes.