Federal law enforcement agents have been using warrantless cell-tower locational tracking of criminal suspects in the wake of the Supreme Court’s ruling 18 months ago that they need probable-cause warrants from judges to affix covert GPS devices to vehicles.

But the law on cell-site locational tracking is all over the books, with judges offering mixed rulings on whether warrants are needed. While dozens of lower courts have ruled on the issue, only two appellate courts have. All of which means some suspects are being convicted based on locational data of what towers their cell phones are pinging, and others are not, because some courts are requiring warrants.

“Only a few courts of appeal have considered this, although a number of lower courts have. They’ve been all over the map,” said Nathan Wessler, an American Civil Liberties Union staff attorney.