NYPD has used cell tracking technology 1,000 times since '08

A cell-site simulator, also known as a Stingray, is a suitcase-

sized device that can sweep up basic cellphone data from a neighborhood by tricking phones into believing it's a cell tower, allowing it to identify unique subscriber numbers. The data are then transmitted to the police, helping them determine the location of a phone without the user even making a call or sending a text message.

Police records show the technology has helped catch suspects in kidnappings, rapes, robberies, assaults and murders. Missing people have been discovered. In some cases, no arrest was made or the phone was located but had been ditched. Officers with warrant squads, robbery squads and homicide units all used the technology, according to the records.

Federal law enforcement in September said it would be routinely required to get a search warrant before using the technology—a first effort to create a uniform legal standard for federal authorities. But the policy applies only to federal agencies within the Justice Department and not, as some privacy advocates had hoped, to state and local law enforcement whose use of the equipment has stirred particular concern and scrutiny from local judges. The NYPD would be required to get a warrant if the investigation was a joint effort with federal officials.

Read more at: https://phys.org/news/2016-02-nypd-cell-tracking-technology.html#jCp