What Is a Search Warrant? When the State May Enter Your Home

The rule in every common-law country is that the police may not enter private property to search it without either the occupier's consent or a warrant, and that a warrant is issued by a magistrate or judge only on sworn information giving reasonable grounds to believe that evidence of a crime will be found in the place named. The warrant must say what place and what is sought; a warrant to search a house for stolen televisions does not permit reading the occupier's letters. The judge is meant to be a check, a person independent of the investigation who can refuse, and the application is made on paper and often at short notice, with the officer swearing to the facts and the magistrate signing or declining. In England the main power is in the Police and Criminal Evidence Act 1984; in the United States it is constitutional, and a search without a warrant is presumed unreasonable.

The tests differ in wording and agree in substance:

• •A specific offence under investigation, not a general wish to look
• •Reasonable grounds, or in America probable cause, to believe that material of value to the investigation is on the premises, based on facts stated under oath rather than suspicion
• •A named place and a described object, so that the search is limited to where the thing might be; officers may look in drawers for a knife but not for a car
• •Reason to think consent would not be given or would defeat the purpose, since a warrant is unnecessary if the occupier will let the police in
• •A time limit, usually three months in England and fourteen days for federal warrants in the United States, and execution at a reasonable hour unless the warrant says otherwise

The warrant rule has exceptions that in practice account for most searches. The police may enter without one to arrest a person they are pursuing, to save life or prevent serious damage, or when a suspect has been arrested and the premises are searched for evidence of that offence; they may search a person or a vehicle on reasonable suspicion of carrying drugs or weapons, since a car can drive away while a warrant is sought; they may seize what is in plain view during a lawful entry; and they may search anything the occupier consents to, which is why the request to have a look round is the commonest search of all and why the answer may be no. Border searches, prisons, schools and the regulatory inspections of restaurants and factories operate under different rules. In terrorism cases the powers are broader and the judicial check thinner, and the argument over how much broader is a permanent one.

The two systems enforce the rule differently. In the United States the exclusionary rule, laid down for federal courts in 1914 and extended to the states in 1961, says that evidence obtained by an unlawful search cannot be used at trial, so that a confession found in a drawer the police had no right to open is inadmissible even if it proves guilt; the rule exists because nothing else was found to deter the police, and its cost, that the guilty sometimes go free, has been debated ever since. English courts have a discretion to exclude unfairly obtained evidence but usually admit it, and the remedy for an unlawful search is a civil claim for trespass and a disciplinary complaint, which critics say is no deterrent at all. Both systems agree that the officer who searches without authority is liable; they disagree about whether the state should also lose what he found.

The doctrine was made for houses and papers, and the questions of the last decade have been about phones and data. In 2014 the American Supreme Court held unanimously that the police may not search the contents of an arrested person's phone without a warrant, since a phone holds more of a person's life than a house ever did, and in 2018 that a warrant is needed to obtain a person's location history from their mobile network. Cloud data, encrypted devices that the owner refuses to unlock, and searches of accounts held by companies in other countries have produced a patchwork of rulings and statutes that is still being assembled. Wilkes's principle, that the state may look only where a judge has been persuaded there is something to find, is being re-argued for a house that fits in a pocket.

The rules on carrying out a warrant are as detailed as those on obtaining one. In England, the codes of practice under the 1984 Act require officers to identify themselves, show the warrant to the occupier and give them a copy, along with a written notice explaining the search powers and the occupier's rights, unless doing so would frustrate the search. Force may be used to get in only when it is necessary, and afterwards the officer endorses the warrant with what was found and seized, so that there is a record the occupier can later check against what was actually taken.

In the United States the equivalent principle is the knock-and-announce rule: officers are normally expected to knock, say who they are and give the occupants a chance to open the door before breaking it down. Judges can authorise a no-knock warrant where announcing would put officers in danger or allow evidence to be destroyed, and these entries have become one of the most argued-about parts of search law, since a sudden forced entry into a home at night can be mistaken for a burglary and has ended in deaths. Several American states and cities have restricted or banned no-knock warrants as a result.

The American colonies had their own grievance alongside the Wilkes affair. Customs officers in Massachusetts hunting for smuggled goods used writs of assistance, general warrants that let them enter any house, shop or warehouse they suspected, naming no place and requiring no evidence. Worse, a writ did not expire when one search was over: it stayed valid for the life of the reigning monarch and six months after. When George II died in 1760 the writs had to be renewed, and in 1761 Boston merchants challenged them before the colony's superior court, with the lawyer James Otis arguing their case.

Otis spoke for around five hours, calling the writs the worst instrument of arbitrary power and arguing that an act against the constitution was void. He lost, and the writs were issued. But a young lawyer watching in the courtroom, John Adams, later wrote that then and there the child Independence was born. When Americans drew up their Bill of Rights three decades later, the Fourth Amendment's demand that warrants particularly describe the place to be searched and the persons or things to be seized was aimed squarely at this kind of open-ended authority, which had followed the colonists into their homes.

In 1762 officials acting on a warrant from a government minister broke into the London home of John Entick, a writer accused of seditious publications, and spent hours searching his papers and carrying many of them away. The warrant was general, naming him but not specifying what could be searched or seized. Entick sued for trespass.

In 1765 the court ruled in his favour, with Lord Camden holding that a minister had no power to issue such a warrant without authority from law, and that if it were otherwise, the papers of every subject could be searched at a minister's pleasure. Entick v Carrington became a foundation of English law on the limits of state power, and it influenced the framers of the American Fourth Amendment.

A search warrant is a judge's written authority for the police to enter a named place and search for described things, granted only on sworn grounds to believe evidence of a specific offence is there, a rule descended from the English general-warrant cases of the 1760s and fixed in the American Fourth Amendment. Arrest, hot pursuit, danger, consent and vehicles are the main exceptions, an unlawful search leads in America to the evidence being excluded and in England mostly to a civil claim, and the same principle is now being applied to phones and data.