They have ruled by 9-0 that a warrant is required to plant a GPS tracker on someone’s car.

The the majority opinion was that  the physical installation of a tracker was a trespass, and hence required a warrant, while 4 justices, Alito, Ginsburg, Breyer, and Kagan argued more broadly that it “impinged on the expectation of privacy.”

This is not a distinction without a difference.  The former position leaves issues like, for example, tracking a cell phone, unclear, and you can be sure that lazy members of the law enforcement community will exploit this ambiguity.