Parameters for modern-day surveillance in the digital age may take shape in key cases the court will decide in 2018. In Carpenter v. United States, officers without a warrant obtained cell-tower data that tracked a drug trafficking suspect's movement. By granting review, the justices showed interest in the erosion of personal privacy when technology keeps track of almost everything people do. The other case, United States v. Microsoft, takes the issue global, asking whether U.S. authorities can access private emails stored on foreign servers.