Law enforcement officials in Washington state will now be required to get a warrant before deploying a stingray, according to a bill that was signed into law by the governor on Monday after unanimously passing both houses of the state legislature.

Washington’s law, which takes effect immediately, is not the first in the United States, but it may impose the most stringent requirements.

A handful of states, including Virginia, Minnesota, and Utah have similar laws on the books. Washington’s, though, imposes extra requirements that compel police to describe the technology and its impact in detail to judges—presumably despite any nondisclosure agreement that those agencies may have with the FBI and the dominant manufacturer of the devices, Harris Corporation. Both the FBI and Harris have previously refused to respond to Ars’ direct questions.

The secretive surveillance devices are not only used to determine a phone’s location, but they can also intercept calls and text messages. During the act of locating a phone, stingrays also sweep up information about nearby phones, not just the target phone. Stingrays typically spoof a cell tower and force phones to connect to it, often by making the handset step down to 2G, which does not require encryption.

Earlier this year, Ars reported on how the FBI is actively trying to "prevent disclosure" of how these devices are used in local jurisdictions across America. Worse still, prosecutors nationwide from St. Louis to Baltimore seem to be more interested in dropping criminal charges rather than revealing details of stingray use.

The bill was introduced earlier this year, just five months after Kate Martin at the Tacoma News Tribune broke the story that not only were Tacoma authorities using stingrays, but local judges did not fully understand the technology.

"If they use it wisely and within limits, that’s one thing," Ronald Culpepper, the presiding judge of Pierce County Superior Court, told the newspaper in August 2014. "I would certainly personally have some concerns about just sweeping up information from non-involved and innocent parties—and to do it with a whole neighborhood? That’s concerning."

Judges like Culpepper were likely signing off on the use of stingrays not based on a warrant application but on a pen register and trap and trace order, a lower legal standard.

It’s relevant because I say so

In the pre-cellphone era, a “pen/trap order” allowed law enforcement to obtain someone's call metadata in near real-time from the telephone company. Now, that same data can also be gathered directly by the cops themselves through the use of a stingray . In some cases, police have gone to judges asking for such a device or have falsely claimed a confidential informant but in fact have deployed this particularly sweeping and invasive surveillance tool.

Most judges are likely to sign off on a pen register application, not fully understanding that police are actually seeking permission to use a stingray. Under both Washington state law and federal law, pen registers are granted under a very low standard: authorities must simply show that the information obtained from the pen register is “relevant to an ongoing criminal investigation”—a far lower standard than being forced to show probable cause for a search warrant or wiretap order.

A wiretap requires law enforcement to not only specifically describe the alleged crimes but also to demonstrate that all other means of investigation had been exhausted or would fail if they were attempted. In the wake of the Tacoma News Tribune’s reporting on stingray use in Tacoma, in November 2014, judges there imposed stricter standards.

The new law has unique language requiring that not only must a probable cause-driven warrant be obtained before a stingray can be deployed but that law enforcement must explain in detail to the judge what exactly is being done.

The American Civil Liberties Union (ACLU), which has long supported more strigent standards surrounding stingrays, said that the new language is crucial.

"The language you point out in the Washington bill is significant because it aims to minimize the detrimental impact on bystanders whose phones are ensnared by a stingray," Nathan Wessler, an ACLU attorney, told Ars by e-mail.

"Also significant is the language requiring full disclosure to the judge of details about how and where the stingray will be used, and its capabilities and expected effect on bystanders. Only with that kind of full and accurate information can judges fulfill their constitutional duty to oversee and constrain law enforcement surveillance activities. The Washington law was prompted by revelations about police use of stingrays in Tacoma without warrants and without informing judges. As similar patterns are uncovered around the country, we expect to see similar legislation introduced elsewhere."

Catherine Crump, a law professor at the University of California, Berkeley, also welcomed the news.

"Stingrays are exactly the sort of invasive surveillance technology for which the warrant requirement was designed," she said by e-mail. "Congress has done little to protect our civil liberties in the face of new technologies."

Mike Katz-Lacabe, a California-based privacy activist, concurred.

"Once again, oversight and legislation is playing catch up to advancements in law enforcement use of surveillance technology," he said by e-mail. "I hope that this will encourage or eventually force the FBI to obtain a warrant for its use of stingrays, which it claims can be used in public places without a warrant."

Earlier this month, the Department of Justice announced that it would be reviewing its stingray policy.