Here's the PDF of the case.
[W]e need not decide whether the officers’ investigation of Jardines’ home violated his expectation of privacy under Katz. One virtue of the Fourth Amendment’s property-rights baseline is that it keeps easy cases easy. That the officers learned what they learned only by physically intruding on Jardines’ property to gather evidence is enough to establish that a search occurred.The dog had gone up onto the porch — that is, the curtilage: "The front porch is the classic exemplar of an area 'to which the activity of home life extends.'"
Justice Kagan (with Sotomayor and Ginsburg) joins Scalia's opinion "in full" and riffs on Scalia's "keeps easy cases easy" by quipping that adding the expectation of privacy analysis would "make 'an easy cas[e] easy” twice over.'"
Alito writes the dissenting opinion. The police came onto the property, but only on "the customary path," during the daytime, and for "less than a minute or two." As for privacy:
A reasonable person understands that odors emanating from a house may be detected from locations that are open to the public, and a reasonable person will not count on the strength of those odors remaining within the range that, while detectible by a dog, cannot be smelled by a human.Alito's opinion is much more dog-positive than Scalia's or Kagan's. Scalia and Kagan refer to "the dog" — it's basically a tool of the police to them. Kagan compares the dog's nose to the "thermal imaging device" in Kyllo. Alito calls the dog by name: Franky. Alito's got footnotes to things like "A Dog's History of America: How Our Best Friend Explored, Conquered, and Settled a Continent."