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Expectation of privacy is a legal test which is crucial in defining the scope of the applicability of the privacy protections of the Fourth Amendment to the United States Constitution. It is related to, but is not the same as, a right to privacy, a much broader concept which is found in many legal systems (see privacy law).
There are two types of expectations of privacy:
Examples of places where a person has a reasonable expectation of privacy are a person's residence or hotel room and public places which have been specifically provided by businesses or the public sector in order to ensure privacy, such as public restrooms, private portions of jailhouses, or a phone booth.
In general, one cannot have a reasonable expectation of privacy in things held out to the public. A well-known example is that there are no privacy rights in garbage left for collection in a public place. Other examples include: pen registers that record the numbers dialed from particular telephones; conversations with others, though there could be a Sixth Amendment violation if the police send an individual to question a defendant who has already been formally charged; a person's physical characteristics, such as voice and handwriting; what is observed pursuant to aerial surveillance that is conducted in public navigable airspace not using equipment that unreasonably enhances the surveying government official's vision; anything in open fields (e.g., a barn); smells that can be detected by the use of a drug-sniffing dog during a routine traffic stop, even if the government official did not have probable cause or reasonable suspicion to suspect that drugs were present in the defendant's vehicle; and paint scrapings on the outside of a vehicle.
The expectation of privacy is crucial to distinguishing a legitimate, reasonable police search and seizure from an unreasonable one.
A "search" occurs for purposes of the Fourth Amendment when the Government violates a person's "reasonable expectation of privacy." In Katz v. United States, 389 U.S. 347 (1967) Justice Harlan issued a concurring opinion articulating the two-prong test later adopted by the U.S. Supreme Court as the test for determining whether a police or government search is subject to the limitations of the Fourth Amendment:
To meet the first part of the test, the person from whom the information was obtained must demonstrate that they, in fact, had an actual, subjective expectation that the evidence obtained would not be available to the public. In other words, the person asserting that a search was conducted must show that they kept the evidence in a manner designed to ensure its privacy.
The first part of the test is related to the notion "in plain view". If a person did not undertake reasonable efforts to conceal something from a casual observer (as opposed to a snoop), then no subjective expectation of privacy is assumed.
The second part of the test is analyzed objectively: would society at large deem a person's expectation of privacy to be reasonable? If it is plain that a person did not keep the evidence at issue in a private place, then no search is required to uncover the evidence. For example, there is generally no search when police officers look through garbage because a reasonable person would not expect that items placed in the garbage would necessarily remain private. An individual has no legitimate expectation of privacy in information provided to third parties. In Smith v. Maryland, 442 U.S. 735 (1979), the Supreme Court held individuals have no "legitimate expectation of privacy" regarding the telephone numbers they dial because they knowingly give that information to telephone companies when they dial a number. Therefore, there is no search where officers monitor what phone numbers an individual dials, although the Congress has enacted laws that restrict such monitoring. The Supreme Court has also ruled that there is no objectively reasonable expectation of privacy (and thus no search) when officers hovering in a helicopter 400 feet above a suspect's house conduct surveillance. The U.S. Court of Appeals for the Sixth Circuit held in 2010 that users did have a reasonable expectation of privacy in the contents of their e-mail in United States v. Warshak, although no other court of appeals has followed suit.
An article by İlker and ÖKTEM (2012) entitled "Expectation of Privacy in Cyberspace: The Fourth Amendment of the US Constitution and an Evaluation of the Turkish Case" starts by giving us operational definitions of concepts of privacy, expectation of privacy, and cyberspace. In providing these definitions, the authors were able to then present what kind of cyberspace they will be addressing and subsequently what time of legality they will talk about to address in an online setting. These definitions served to have a better understating of how they all work together. The authors identify that there needs to be policy to address privacy in the cyberspace. The article evaluates the extent of the law and how it can protect people's expectations of privacy within the cyber environment. The article talks about privacy expectations in cyberspace while discussing the Fourth Amendment of the United States constitution. The Fourth Amendment provides citizens of the United States with security of themselves, their house, and from unreasonable searches and seizures. If these are violated, there are reasonable sanctions for the violating party.
However, the article points out that the Fourth Amendment does not protect individuals from informational privacy. It has been established that since the government can seize any item then it is able to obtain access to the information they want or need. The article focuses and tells us that the Fourth Amendment and how it applies to decrypting an internet communication and how it cannot trespass the reasonable expectation of privacy. In other words, this type of communication cannot violate the Fourth Amendment rights. Finally, the article presents the state of privacy during the time it was written and compares to the privacy in the Turkish judicial systems. The authors take particular notice to how there needs to be a strong political desire to secure privacy issues in society specifically in cyberspace.
In Florida v. Jardines the U.S. Supreme Court ruled on March 26, 2013, that police violated the Fourth Amendment rights of a homeowner when they led a drug-sniffing dog to the front door of a house suspected of being used to grow marijuana.
In a 5-to-4 decision, the court said that police conducted a "search" when they entered the property and took the dog to the house's front porch. Since the officers had not first obtained a warrant beforehand, their search was unconstitutional, the court said. The court said the police officers violated a basic rule of the Fourth Amendment by physically intruding into the area surrounding a private home for investigative purposes without securing a warrant.
"When it comes to the Fourth Amendment, the home is first among equals," Justice Scalia wrote. "At the amendment's very core stands the right of a man to retreat into his own home and there be free from unreasonable government intrusion." Scalia added: "This right would be of little practical value if the state's agents could stand in a home's porch or side garden and trawl for evidence with impunity."
This case may provide some argument or protection in the area of reasonable expectation of privacy in one's home and curtilage given the rapid advancement of drone technology, particularly given law enforcements' stated intent to deploy these technologies. This question may well turn on the court's interpretation of the "naked eye" test (described in the earlier Ciraolo case) in relation to the "enhanced view" test. It would seem enhanced view(s) are achievable through the use of drone technology. See also: Kyllo v. United States, 533 U.S. 27 (2001) (precludes enhanced views from outside a home without a warrant, using thermal imaging).
In Missouri v. McNeely on April 17, 2013, The U.S. Supreme Court ruled that police must generally obtain a warrant before subjecting a drunken-driving suspect to a blood test. The vote was 8-to-1, with Justice Clarence Thomas the lone dissenter.
The legal case of R v Tessling the Supreme Court of Canada identified that the defendant did not have a reasonable expectation of privacy with regards to the information policemen acquired from him. These officers obtained this information by using warrantless infrared imaging to monitor the respondent's home. The court tried to answer the questions of what can be expected to be covered by reasonable expectation of privacy. They specify that information that is covered under reasonable expectation of privacy is called "deeply personal information." Matheson (2008) offers the view that deeply personal information can be related to sensitivity. One common functional use to describe privacy and personal information is a matter of control. This type of information is to be treated within the choice of the individual that holds the information. However, the difference between deeply personal information and other information is that this particular type of information tends to be related to how vulnerable and sensitive an individual is to the exposure of said information. Matheson (2008) tells us that it is particularly deemed deeply personal information if the personal information would weaken the individual's account or personal story about himself or others if shared. Matheson (2008) states that while questionable the Canadian Court's decision was partly right because the defendant did not have a reasonable expectation of privacy when it came to the warrantless infrared search.