By now most Americans agree that the NSA surveillance program, brought to light by leaked documents from former NSA contractor Edward Snowden, went “too far.” Just because the spy agency could keep tabs on every American, did not mean it should. The price of surveillance technology, however, had dropped so precipitously over the last two decades that once the agency overcame any

moral objections it had about the program, few practical considerations stood in its way of implementing a system that could monitor 315 million Americans every day. Indeed, one estimate tagged the NSA’s annual surveillance costs at $574 per taxpayer, amounting to a paltry six-and-a-half cents an hour. ="#!1624ea24-b455-4345-a55f-db872b21ea6f">

If privacy law experts Kevin S. Bankston and Ashkan Soltani are correct, costs, once a significant check on government spying and police monitoring efforts, have become an afterthought. In a recent study published in the Yale Law Journal Online, Bankston and Soltani found that most technologies deployed for mass-surveillance efforts by police departments (e.g., GPS devices and domestic drones) exhibit similar cost structures to the NSA spying program: as the number of subjects increase, the cost of keeping tabs each target nears zero. Cheaper, more effective tracking devices have been a boon to cash-strapped police departments nationwide, largely to the dismay of civil-liberties groups.

Meanwhile, privacy protections afforded to individuals under the Fourth Amendment, the cornerstone of our privacy rights that safeguards individuals from unreasonable searches and seizures by the state, have been eroding for years. Whether a particular search or seizure is deemed ‘reasonable’—thus justifying police action—rests largely on our ephemeral notions of privacy. It’s a dicey standard. As we place more of our private lives in the public domain (73 percent of adults online use social media), we, as well as courts, consider fewer acts to be truly private and thus protected by the constitution. At the height of McCarthyism in the 1950s, for instance, groups fought tooth-and-nail to keep library lists private; today we publicize the titles of books we’ve recently read on sites like Facebook and Goodreads.

Practical considerations, like costs, Bankston and Soltani argue, have long provided structural defenses that have buffeted the sliding privacy standard embedded in the Fourth Amendment. Imagine, in the 1800s ten constables surreptitiously tailing one suspect through the winding streets of Philadelphia; by the 1940s the same task still took eight officers in four police cars to accomplish. Monitoring each suspect was costly. “Only an investigation of unusual importance,” according to Justice Samuel Alito, “could have justified such an expenditure of law enforcement resources.”

Today, however, diminished privacy expectations coupled with limited cost-constraints for law enforcements surveillance activities have emboldened police departments to push the limits of new tracking technologies and techniques with little regard for privacy rights or chances of successful prosecution. A 2012 survey of police chiefs found that 83 percent of departments use GPS devices to track suspects and most respondents “expect to increase the practice of placing GPS devices on crime suspects’ vehicles.” The same survey found that “89 percent of agencies said they monitor social media to identify investigative leads—for example, reviewing Facebook or Twitter pages”. In New York City, of the 4.4 million people questioned by police as part of the department’s recently defunct stop-and-frisk surveillance program, only eleven percent of the encounters resulted in an arrest or summons, according to an analysis by the NYCLU.

To realign the “equilibrium of power” between police and citizens, Bankston and Soltani propose a bright-line, cost-based rule designed to augment the current chimerical reasonable expectation standard employed by courts today: if a new technology makes it ten times cheaper for law enforcement to monitor a target, that technology violates the Fourth Amendment’s reasonable expectation of privacy standard and cannot be used without a court-issued warrant.

“When new technologies expand law enforcement’s capabilities, the law does (and should) respond by placing new limits on government; when new technologies give criminals a leg up, the law does (and should) respond by loosening the government’s reins,” they write.

In United States v. Jones, five Supreme Court Justices held that a man’s reasonable expectation of privacy was breached after police tracked his movements on public roads for 28 days using a GPS device. The majority in the 2012 opinion, however, stopped short of articulating a clear rule other than Justice Alito’s finding that “the line was surely crossed before the 4-week mark.”

Using the Jones ruling as a baseline, Bankston and Soltani proceeded to calculate and compare the costs of different location tracking methods used by police. Traditional surveillance methods like covert foot and car pursuits cost $250 and $275, respectively, per hour per target, according to their estimates. Another common method, which the Supreme Court has approved, involves two agents tracking a suspect’s movements from their police vehicle through a radio-based transmitter affixed to a target’s car or slipped in his bag at a cost of $105 to $113 per hour.

Newer surveillance technologies, however, were significantly cheaper when costs were tabulated on an hourly basis. The total price tag of tracking a suspect using a GPS device, similar to the one in Jones for instance, came out to $10 an hour over one day, $1.43 per hour over a week and $0.36 per hour over a month. Another relatively new technique, obtaining a suspect’s location through their cell phone signal with the carrier’s assistance, yielded similar results. As of August 2009, fees for obtaining cell phone location data from carriers ranged from $0.04 to $4.17 per hour for one month of surveillance. (Sprint, for example, charges $30 per month per target while T-Mobile charges $100 per day).

After tabulating their results, Bankston and Soltani concluded that the total cost of using a GPS device to track as suspect over twenty-eight days (the method rejected in Jones) was roughly three hundred times less expensive than the same tracking using a transmitter (technology approved by the Supreme Court) and 775 times less expensive than using the five car pursuit method (also approved). Meanwhile, the cost of using transmitter-surveillance technology was only 2.5 times less expensive than undercover car pursuit.

In advocating their cost based-approach for determining the legality of different surveillance technologies, the researchers maintain that they do not “equate police efficiency with unconstitutionality” but rather attempt to preserve the degree of privacy that existed at during the Framer’s era. “Improvements to police efficiency are desirable, but radical increases in police power due to rapid technological change—without additional legal constraints to prevent abuse—are not,” they state.

As data mining, wiretaps and domestic drones become the new norm for police departments at a cost of a few cents a day, we need to begin to have a frank discussion about the trajectory of our Fourth Amendment protections just to maintain the current levels of privacy safeguards. A cost-based approach is a start by providing courts with an objective standard to measure the intrusiveness of new surveillance technologies. As Justice Alito quipped in Jones, we must remember that absent “a very tiny constable…with [the] incredible fortitude and patience” hiding out in the trunk of a carriage, it would have been impossible for George Washington’s colonial law enforcement authorities to have carried out anything near the level of surveillance that today’s police forces can do at the drop of a dime.

Drew F. Cohen is a former law clerk to the chief justice of the Constitutional Court of South Africa. Follow him on Twitter at @DF_Cohen or email him at [email protected].

Image: Wikimedia Commons/RIA Novosti archive, image #439194 / Igor Zarembo / CC-BY-SA 3.0.