On Friday, the Supreme Court issued a long-awaited opinion in Carpenter v. United States. The Court held that when law enforcement obtains long-term cell site location information from a suspect’s service provider, it conducts a Fourth Amendment search that normally requires a warrant. Although the majority opinion states that it “is a narrow one,” the dissenting Justices and some scholars see it as a seismic shift that may have many aftershocks. I’ll summarize the case and then use former Secretary of Defense Donald Rumsfeld’s famous approach to address the “known knowns,” the “known unknowns,” and the “unknown unknowns” after Carpenter.