Carpenter v. United States is a landmark Supreme Court case that established the Fourth Amendment's protection against unreasonable searches and seizures. The case involved Timothy Carpenter, who was convicted of multiple counts of robbery and firearms offenses. The government had obtained Carpenter's cell phone records without a warrant, which it used as evidence against him. Carpenter argued that the government's acquisition of his cell phone records without a warrant violated his Fourth Amendment rights. The Supreme Court agreed, ruling that the government's acquisition of Carpenter's cell phone records constituted a search and seizure, and that the government must obtain a warrant before accessing such records. The Court held that the Fourth Amendment requires the government to obtain a warrant based on probable cause before accessing an individual's cell phone records. The Court's ruling in Carpenter v. United States has had a significant impact on Fourth Amendment jurisprudence. It established that individuals have a reasonable expectation of privacy in their cell phone records, and that the government must obtain a warrant before accessing such records. The ruling has also been used to extend Fourth Amendment protections to other forms of digital data, such as emails and text messages.

Justice Sotomayor wrote the dissenting opinion in Carpenter v. United States, arguing that the majority’s decision to allow law enforcement access to cell phone location data without a warrant was an unconstitutional violation of privacy rights. She argued that this type of information is highly personal and sensitive, and should be protected from government intrusion under the Fourth Amendment. Furthermore, she noted that advances in technology have made it easier for governments to track individuals' movements over time with little effort or cost on their part; thus, allowing such surveillance without a warrant would open up citizens to potential abuse by authorities. Justice Sotomayor concluded her dissent by stating that “the Government's unrestrained power to assemble data...is antithetical to democratic governance” and urged Congress or state legislatures take action if they wish for such surveillance powers exist within our society.