“When deployed, StingRay forces any cell phones in the area to send it a signal, the same way that a phone normally sends a signal to cell towers. Even if a cell phone is not in use, it still transmits its phone number and electronic serial number to the device.
Once a tool used by federal officials for combating terrorism, in the last decade StingRay-type devices have been approved for use by local law-enforcement agencies. Officers have been using the technology under the purview of the FBI — and only under strict orders not to disclose anything about it, even in court.”