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.[2] Other examples include: pen registers that record the numbers dialed from particular telephones;[4] 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;[5] a person's physical characteristics, such as voice and handwriting;[6] 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;[7][8] anything in open fields (e.g., a barn);[9] 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;[10] and paint scrapings on the outside of a vehicle.[11]
