This a great article about how one very determined man, Daniel Rigmaiden, who knew he’d been sprung by some form of hidden surveillance technology that spied on cellphone signals, exposed the technology known as the Stingray:
To track Rigmaiden down, the investigators had used a secret device, one that allowed them to pinpoint their target with far more accuracy than Verizon could. They called it a cell-site simulator, or by its trade name, Stingray. Neither term was found in the court order that authorized its use. The device had to be kept secret, even from the courts.
End of quote.
It is in widespread use in the US and probably globally, though probably now superseded, as the article suggests. Its use was long suppressed by the police, the FBI and prosecutors and was being widely used without a warrant. Rigmaiden’s work has brought it out into the open.