Still, is the Justice Department’s airborne dragnet program legal? The answer is “maybe.”
Federal authorities have employed similar tools in the past. The Federal Bureau of Investigation is known to use a surveillance tool called a “stingray,” a portable transceiver that tricks cell phones within a certain area into relaying their locations, not unlike the equipment onboard the Marshals’ aircraft. A government vehicle with a stingray can net hundreds of nearby cell phones’ approximate locations just by driving through a typical neighborhood. The government has said it doesn’t need a probable cause warrant to use stingrays because investigators don’t collect the content of phone calls, just the locations of those phones. Government officials, meanwhile, have said they get court approval to use the devices.
Much of the government’s warrantless use of stingray-style technology hinges on a 1979 Supreme Court decision titled Smith v. Maryland. Smith involved law enforcement’s use of a device called a pen register that, when attached to a suspect’s phone line, recorded the numbers of outgoing calls, but not the calls themselves. The Smith decision upheld the warrantless use of such devices because the suspect’s phone company would record the same data picked up by the pen register, and therefore the suspect had no reasonable expectation of privacy when it came to that information. Currently, the law requires a court to approve the use of a pen register, but investigators only have to show that the device’s use is “relevant to an ongoing criminal investigation,” a much weaker standard than a probable cause warrant requires.