The majority held that by physically installing the GPS device on Jones's car, the police had committed a trespass against his "personal effects".

[2] During the course of the investigation, police installed a Global Positioning System (GPS) device on Jones's wife's Jeep Grand Cherokee.

[7] Jones argued that his criminal conviction should be overturned because the use of the GPS tracker violated the Fourth Amendment's protection against unreasonable search and seizure.

[12][13] In 2007, Judge Richard Posner of the United States Court of Appeals for the Seventh Circuit had reached the opposite conclusion on whether GPS tracking by police was a search under the Fourth Amendment.

The second question was "Whether the government violated respondent's Fourth Amendment rights by installing the GPS tracking device on his vehicle without a valid warrant and without his consent.

[17] Dreeben cited United States v. Knotts (1983) as an example in which police were allowed to use a device known as a "beeper" that enabled tracking a car from a short distance away.

[17] Chief Justice John Roberts distinguished the present case from Knotts, saying that using a beeper still took "a lot of work" whereas a GPS device allows the police to "sit back in the station ... and push a button whenever they want to find out where the car is.

"[21] Justice Sonia Sotomayor noted that "What motivated the Fourth Amendment historically was the disapproval, the outrage, that our Founding Fathers experienced with general warrants that permitted police indiscriminately to investigate just on the basis of suspicion, not probable cause, and to invade every possession that the individual had in search of a crime."

He cited a line of cases dating as far back as 1886 to argue that a physical intrusion, or trespass, into a constitutionally-protected area – in an attempt to find something or to obtain information – was the basis, historically, for determining whether a "search" had occurred under the meaning of the Fourth Amendment.

[29] However, he cited a number of post-Katz cases including Alderman v. United States[30] and Soldal v. Cook County[31] to argue that the trespass analysis had not been abandoned by the Court.

Even during short-term monitoring, she reasoned, GPS surveillance can precisely record an individual's every movement, and hence can reveal completely private destinations, like "trips to the psychiatrist, the plastic surgeon, the abortion clinic, the AIDS treatment center, the strip club, the criminal defense attorney, the by-the-hour motel, the union meeting, the mosque, synagogue or church, the gay bar and on and on".

Specifically, he argued that the common law property-based analysis of a "search" under the Fourth Amendment did not apply to such electronic situations as the one that occurred in this case.

[45]Following the privacy-based approach most commonly used post-Katz, the other four justices were instead of the opinion that the continuous monitoring of every single movement of an individual's car for 28 days violated a reasonable expectation of privacy, and thus constituted a search.

Alito explained that before GPS and similar electronic technology, month-long surveillance of an individual's every move would have been exceptionally demanding and costly, requiring a tremendous amount of resources and people.

[46] With regard to continuous monitoring for a short period, the other Justices relied on the Knotts precedent and declined to find a violation of the expectation of privacy.

[49] Criminal defense attorneys and civil libertarians such as Virginia Sloan of the Constitution Project praised the ruling for protecting Fourth Amendment rights against government intrusion through modern technology.

[48] The Electronic Frontier Foundation, which filed an amicus brief arguing that warrantless GPS tracking violates reasonable expectations of privacy, praised Sotomayor's concurrence for raising concerns that existing Fourth Amendment precedents do not reflect the realities of modern technology.

[59][60] In October 2013, the Court of Appeals for the Third Circuit addressed the unanswered question of whether warrantless use of GPS devices would be reasonable — and thus lawful — under the Fourth Amendment if police have probable cause to justify the search.