In a fairly stunning win for mobile phone privacy, the Supreme Court has ruled that law enforcement agencies must obtain a warrant before they can demand and receive from mobile carriers and mobile providers access to the cell phone location data (known as ‘cell site location information’, or CSLI for short) of a given cellular phone. In the case of Carpenter v. United States, the Supreme Court held that tracking a cell phone is barely different than putting an ankle bracelet on an individual and monitoring their movements, and so overturned related case law that has been around for (up to) decades.