In United States constitutional law, 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 U.S. 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). Overall, expectations of privacy can be subjective or objective.
Overview
There are two types of expectations of privacy: Subjective expectation of privacy: a certain individual's opinion that a certain location or situation is private which varies greatly from person to person Objective, legitimate, reasonable expectation of privacy: an expectation of privacy generally recognized by society and perhaps protected by law.
Places where individuals expect privacy include residences, hotel rooms, or public places that have been provided by businesses or the public sector to ensure privacy, including public restrooms, private portions of jailhouses, or phone booths. This expectation extends against both physical and digital intrusions, and even cell tower geolocation data is protected.
In general, one cannot have a reasonable expectation of privacy for things put into a public space. 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 sends 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.
While a person may have a subjective expectation of privacy in his/her car, it is not always an objective one, unlike a person's home. Expectation of home privacy extends to thermal imaging.
The expectation of privacy concept also applies civilly whereas the unreasonable violation of which may result in mental distress rather than incarceration. Civil privacy expects against: (1) intrusion upon seclusion or solitude, or into private affairs; (2) public disclosure of embarrassing private facts; (3) publicity which places a person in a false light in the public eye; and (4) appropriation of name or likeness.
Privacy and search
The expectation of privacy is crucial in 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, 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: Governmental action must contravene an individual's actual, subjective expectation of privacy Expectation of privacy must be reasonable, in the sense that society in general would recognize it as such
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.