A sharply divided Kentucky Supreme Court ruled Thursday that police violated a robbery suspect’s constitutional protections by accessing his cellphone without a warrant, calling use of the phone as a tracking device “profoundly invasive.”

In the 4-3 decision, the court’s majority said the robbery suspect was subjected to a warrantless search when police obtained his real-time cellphone location information. They ruled that the information was illegally acquired and should be excluded from evidence.At issue was whether there’s a “reasonable expectation of privacy” regarding a person’s real-time cell-site location information, also known as CSLI, under federal Fourth Amendment protections against unreasonable searches and seizures. Such information can be used to determine a cellphone’s location with “near perfect accuracy” when the phone is powered on, the court noted.

“In obtaining an individual’s cell phone’s real-time CSLI, police commandeer the cell phone and its transmissions for the purpose of locating that individual,” Chief Justice John D. Minton Jr. said in writing for the majority. “We find this usurpation of an individual’s private property profoundly invasive, and we liken it to a technological trespass.”

The ruling stems from a case in Kentucky’s Woodford County involving robbery suspect Dovontia Reed. One of his attorneys hailed it a far-reaching victory for civil liberties.