A search warrant is a court order that a magistrate, judge or Supreme Court official issues to authorize law enforcement officers to conduct a search of a person, location, or vehicle for evidence of a crime and to confiscate any evidence they find. In most countries a search warrant cannot be issued in aid of civil process.
Jurisdictions that respect the rule of law and a right to privacy constrain police powers, and typically require search warrants or an equivalent procedure for searches police conducted in the course of a criminal investigation. The laws usually make an exception for hot pursuit: a police officer following a criminal who has fled the scene of a crime has the right to enter a property where the criminal has sought shelter. This contrasts with authoritarian regimes, where police typically can search property and people without having to provide justification or secure court permission.
In the United Kingdom, a local magistrate issues search warrants, which require that a constable provide evidence that supports the warrant application. In the majority of cases where police already hold someone in custody, police can search premises[clarification needed] without a search warrant under Section 18 of the Police and Criminal Evidence Act (PACE), which requires only the authority of an inspector.
Under Section 18(5)a of PACE, a constable can conduct a search immediately without an inspector's authorisation. This subsection allows a constable to search the home of a suspect(s) under arrest in their presence before they take the suspect to a police station (or other custody location). Under Section 32 of PACE, a constable who arrests a person who is on their own property or has just left their premises, may immediately search both the suspect and the immediate area.
Under the Fourth Amendment to the United States Constitution, most police searches require a search warrant based on probable cause, though 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 specify the object to search for and the place to search for it. Other items, rooms, outbuildings, persons, vehicles, etc. may require additional search warrants.
To obtain a search warrant, an officer must prove to a magistrate or judge that probable cause exists based upon direct information (i.e., the officer's personal observation) or hearsay information. Hearsay information can even be obtained by oral testimony given over a telephone or from an anonymous or confidential informant, so long as probable cause exists based on the totality of the circumstances. Police can seize both property and persons 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 evidence police collect without a search warrant may not be sufficient to convict, but may be sufficient to suggest that a warrant would allow police to find enough evidence to convict.
In the United States, the issue of federal warrants is determined under Title 18 of the United States Code. The law has been restated and extended under Rule 41 of the Federal Rules of Criminal Procedure. Federal search warrants may be prepared on Form AO 93, Search and Seizure Warrant. Each state also enacts its own laws governing the issuance of search warrants.
Police do not need a search warrant, or even probable cause, to perform a limited search of a suspect's outer clothing for weapons, if police have a reasonable suspicion to justify the intrusion—a Terry "stop and frisk".
A customs officer of the United States is not required to have a warrant, reasonable suspicion, or consent to search persons, vehicles, baggage, or cargo that have border nexus,[clarification needed] regardless of citizenship or origin.
Certain cases don't require a search warrant, such as where a person in control of the object or property gives consent. Some commonly cited exigent circumstances are: hot pursuit of a felon (to prevent a felon's escape or ability to harm others); imminent destruction of evidence before a warrant can be properly obtained; emergency searches (such as where someone is heard screaming for help inside a dwelling); or a search incident to arrest (to mitigate the risk of harm to the arresting officers specifically).
Another exception is when evidence is in plain view. In such a case, the officer is legitimately on the premises, his observation is from a legitimate vantage point, and it is immediately obvious that the evidence is contraband. The plain view rule applies—for example—when the officer has pulled the suspect over for a seat belt violation and sees a syringe full of heroin on the passenger seat.
As first established by Carroll v. United States, police are allowed to search a vehicle without a search warrant when they have probable cause to believe that evidence or contraband is located in a vehicle. When police arrest an individual shortly after the individual has exited a vehicle, the police may conduct a full search of the suspect's person, any area within that person's immediate reach, and the passenger compartment of the recently occupied vehicle for weapons or any other contraband. However, Arizona v. Gant limits such searches to circumstances where the arrested person could have accessed the vehicle, or when the vehicle could contain evidence of the crime the person is arrested for.
If the subject is arrested in a home, police may search the room where they arrested the subject, and conduct a "protective sweep" of the premises if they reasonably suspect that other individuals may be hiding. The laws also allow searches in emergencies where the public is in danger.
With rented property, a landlord may refuse to allow law enforcement to search a tenant's apartment without a search warrant, and police must obtain a warrant under the same guidelines as if it were a tenant's own home. In some jurisdictions, police may search a hotel room with permission of hotel management but without permission of the guest and without a warrant.
A sneak and peek search warrant (officially called a delayed notice warrant and also a covert entry search warrant or a surreptitious entry search warrant) is a search warrant authorizing the law enforcement officers executing it to effect physical entry into private premises without the owner's or the occupant's permission or knowledge and to clandestinely search the premises.
In California, the California Electronic Communications Privacy Act mandates that in certain cases concerning electronic search warrants that the court issue gag orders "[...] prohibiting any party providing information from notifying any other party that information has been sought [...]".
- Arrest warrant
- National Security Letter
- No-knock warrant, to enter a property without occupant notification
- Sneak and peek warrant, to clandestinely look inside a property
- Sugar bowl (legal maxim)
- Writ of Assistance
- Parallel construction - the untruthful description of the origins of evidence, to avoid laws about search or otherwise
- Farin (29 April 2010). "Breaking and metering". BBC Watchdog. Retrieved 27 October 2012.
British Gas are legally entitled to enter anyone's home if the householder hasn't paid the bill and won't let them in, but they need a warrant from a magistrate, who must be satisfied the information British Gas shows them is correct. In most cases, British Gas also must have issued a prior warning.
- AO 93 (Rev. 12/09) Search and Seizure Warrant. Uscourts.gov.
- 19 CFR 162.6 - Search of persons, baggage, and merchandise.
- Groh v. Ramirez, 540 U.S. 551, 564-65 (2004)
- >Regini, L. A. (July 1999). "The Motor Vehicle Exception: When and Where to Search." FBI Law Enforcement Bulletin. 68, 27-33.
- Hendrie, E. (August 2005). "The Motor Vehicle Exception." FBI Law Enforcement Bulletin, 74.
- Arizona v. Gant, No. 07-542, Decided April 21, 2009: 
- http://www.encyclopedia.com/doc/1G1-98253659.html Archived June 28, 2011 at the Wayback Machine
- California Electronic Communications Privacy Act § 1, codified at California Penal Code § 1546.2. "(b)(1) When a warrant is sought or electronic information is obtained in an emergency under Section 1546.1, the government entity may submit a request supported by a sworn affidavit for an order delaying notification and prohibiting any party providing information from notifying any other party that information has been sought. The court shall issue the order [...]"