United States of America
Under the Fourth Amendment to the United States Constitution, most searches by the police require a search warrant based on probable cause, although there are exceptions. Any police entry of an individual's home always requires a warrant (for either search or arrest), absent exigent circumstances, or the free and voluntary consent of a person with reasonably apparent use of or control over the property.
Under the Fourth Amendment, searches must be reasonable and specific. This means that a search warrant must be specific as to the specified object to be searched for and the place to be searched. Other items, rooms, outbuildings, persons, vehicles, etc. may require additional search warrants.
In the U.S. state of Indiana following a decision by the Indiana Supreme Court, residents no longer have the right to resist unlawful (i.e. without permission, without a warrant) police entry into their homes. Following a 3-2 decision Justice Steven David disclosed his belief that "a right to resist an unlawful police entry into a home is against public policy and is incompatible with modern Fourth Amendment jurisprudence." [1]
To obtain a search warrant, an officer must first prove that probable cause exists before a magistrate or judge, based upon direct information (i.e. obtained by the officer's personal observation) or hearsay information. Hearsay information can even be obtained by oral testimony given over a telephone, or through an anonymous or confidential informant, so long as probable cause exists based on the totality of the circumstances. Both property and persons can be seized under a search warrant. The standard for a search warrant is lower than the quantum of proof required for a later conviction. The rationale is that the evidence that can be collected without a search warrant may not be sufficient to convict, but may be sufficient to suggest that enough evidence to convict could be found using the warrant.
