A federal judge’s decision requiring the government to get a court warrant before obtaining mobile-phone location data is one of a string of conflicting opinions on the topic. It comes as lawmakers and the Supreme Court weigh in on the hot-button issue of locational privacy.

U.S. District Judge Nicholas Garaufis ruled on Tuesday that the government can only acquire cellphone location data on a surveillance target with a full-blown “probable cause” warrant from a judge. The government had argued that it’s entitled to the data whenever it’s “relevant” to a criminal investigation — a lower standar...