Carpenter v. United States (2018): the Supreme Court held that getting seven days of a person's cell phone location history is a search that requires a warrant. It did not rule on plate readers.
Having mapped the cell phone's movements over the course of 127 days, the Government's acquisition of the cell-site records was a search under the Fourth Amendment, and a warrant supported by probable cause was required. […] We do not disturb the application of Smith and Miller or call into question conventional surveillance techniques and tools, such as security cameras.
pp. 22, 21
Carpenter v. United States (2018): the Supreme Court held that getting seven days of a person's cell phone location history is a search that requires a warrant. It did not rule on plate readers.