A government watchdog has found that the Secret Service and ICE’s Homeland Security Investigations (HSI) unit repeatedly failed to obtain the correct legal paperwork when carrying out invasive cell phone surveillance.

The findings were published last week by Homeland Security’s inspector general, tasked with oversight of the U.S. federal department and its many law enforcement units, which said that the agencies often used cell-site simulators without obtaining the appropriate search warrants.

Cell-site simulators — commonly known as “stingrays” — are surveillance gear used by law enforcement that impersonate cell towers to trick nearby cell phones into connecting to them, allowing police to track their real-time location. Some newer stingrays are believed to be capable of capturing the calls and SMS text messages of nearby phones.

But stingrays are controversial because they also ensnare every other device within their range, including devices owned by people with no connection to crime. Stingrays are also developed under strict nondisclosure agreements, which broadly restricts what is publicly known about stingrays, or even what police can disclose about them. Prosecutors have dropped court cases rather than risk revealing proprietary technical details about how cell-site simulators work.

Because of how invasive cell-site simulators are, the inspector general said that federal agencies must first obtain a search warrant, authorized by a judge, before a cell-site simulator can be used. The inspector general said only exigent or emergency circumstances allow for warrantless use of cell-site simulators, which can range from having to act quickly to prevent the destruction of evidence, through to an immediate risk or danger to life, a national security threat or a cyberattack. In those cases, the authorities have to apply for a court order within 48 hours of deploying the cell site simulator — or run the risk of falling foul of the law for carrying out illegal surveillance.

In its redacted report, the inspector general said that the Secret Service and ICE HSI “did not always obtain court orders” as required by their own agency’s policies or federal law.

The watchdog’s report described two sets of problems. The first is that the Secret Service and ICE HSI “did not correctly interpret” the internal policies governing the use of cell-site simulators in emergency situations. In one case, ICE HSI said it did not believe it needed a warrant because a party had “provided consent.”

The other problem was how the Secret Service and ICE HSI used cell-site simulators to support requests from local law enforcement agencies. In one case highlighted by the inspector general, a county judge “did not understand” why prosecutors sought an emergency surveillance order because, not understanding the statute, the judge “believed it to be unnecessary,” leading to a raft of warrantless deployments. In at least one other case, the inspector general rebuked ICE HSI as it was “unable to provide evidence” it ever applied for an emergency court order in one case deemed an exigent circumstance.

Both the Secret Service and ICE HSI accepted the watchdog’s six recommendations, which included shoring up its internal policies and procedures.

The redacted report did not reveal the number of times cell-site simulators were deployed in recent years. U.S. Immigration and Customs Enforcement, or ICE, which enforces immigration law and carries out deportations, is known to have used stingrays hundreds of times between 2017 and 2019.

In a blog post, digital rights group the Electronic Frontier Foundation criticized the report’s redactions. “The OIG should release this information to the public: knowing the aggregate totals would not harm any active investigation, but rather inform public debate over the agencies’ reliance on this invasive technology,” wrote EFF policy analyst Matthew Guariglia.

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