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; 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 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 (for example, 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.
