The devices are small enough to fit in an undercover vehicle. The device creates a very strong but fake cell tower signal which causes phones nearby (perhaps in the whole neighborhood) to connect to it. When the phones connect, the device then captures a lot of personal information. This is particularly helpful to police when they suspect a certain person of say dealing drugs, and know where he is, but don't know his phone number, because he gets a new throw-away phone every few weeks. But it's problematic because the device is capturing the same personal information from all phones in the area. It's a dragnet.
Put another way:
[stingray devices] are used to locate a suspect's phone but in the process, capture phone numbers and data from the cell phones of everyone in the neighborhood. A stingray device simulates a cell phone tower and by its strength, tricks all cell phones in the area into using it. Since it's not really a cell phone tower, the cell phone's information goes right to the stingray device.
Law enforcement has taken the position the stingray is just an enhanced pen register which only requires a court order, not a warrant based on probable cause. In my cases, they've at least gotten a warrant for the device. But do their affidavits and warrant applications advise the Judge that a stingray will be used, which captures the phone data of innocent persons nearby? And if so, does the affidavit or application inform the judge what steps they will take to avoid keeping or examining the data of phones who just happen to be near the target phone at the time they are conducting their search?
The Government typically relies on the exigent circumstances, good faith or inevitable discovery exceptions to the warrant requirement to justify the use of these dragnet devices.
How much do taxpayers spend for police to use these devices? According to the CBS article linked at the top:
A December 2016 report from the House Oversight and Government Reform Committee found U.S. taxpayers spent $95 million on 434 cell-site simulator devices between 2010 and 2014, with the price tag for a single device hovering around $500,000.
"While law enforcement agencies should be able to utilize technology as a tool to help officers be safe and accomplish their missions, absent proper oversight and safeguards, the domestic use of cell-site simulators may well infringe upon the constitutional rights of citizens to be free from unreasonable searches and seizures, as well as the right to free association," the report said.
For more on Stingray Devices, check out the articles cited by the Court in a footnote in the Prince opinion:
The "StingRay" is a popular cell-site simulator produced by the Harris Corporation. See Stephanie K. Pell & Christopher Soghoian, Your Secret Stingray’s No Secret Anymore: The Vanishing Government Monopoly over Cell Phone Surveillance and Its Impact on National Security and Consumer Privacy, 28 Harv. J.L. & Tech. 1, 14 (2014). The name has become a generic term for a cellsite simulator. Kim Zetter, Hacker Lexicon: Stingrays, the Spy Tool the Government Tried, and Failed, to Hide, Wired (May 6, 2016).
