The New York Civil Liberties Union had sued the NYPD in 2016 for specific information on its Stingray program after a records request under the state's Freedom of Information Law was denied.
On Wednesday, a judge ruled the information should remain confidential, saying that disclosing it would help wrongdoers evade detection.
An NYCLU attorney said it may appeal.
The suitcase-sized devices can sweep up cellphone data from an entire neighborhood. Some can even intercept texts and calls.
About a dozen states now have laws requiring warrants to use the technology. A judge in New York City last year ruled the NYPD must have an eavesdropping warrant to use the device.