Introduction

As Judge Richard Posner once said, “Technological progress poses a threat to privacy by enabling an extent of surveillance that in earlier times would have been prohibitively expensive,” thereby “giving the police access to surveillance techniques that are ever less expensive and ever more effective.”1Among these “‘fantastic advances’”2 in surveillance technology is the Global Positioning System (GPS), which provides law enforcement with an inexpensive means to track the precise geographic locations of criminal suspects. The Supreme Court recently addressed this technology in United States v. Jones, which considered whether the police’s attachment of a GPS device to a suspect’s car, and the use of that device to monitor the car’s movements along public roads for twenty-eight days, constituted a search under the Fourth Amendment.3

All nine Justices answered that question in the affirmative, but they produced three different opinions. Five Justices, in an opinion authored by Justice Scalia, did not rule on the question of whether the monitoring of Jones’s movements via the GPS device constituted a search. Rather, the majority found that the attachment of the device to Jones’s car violated his Fourth Amendment expectation of privacy under a trespass-oriented theory of Fourth Amendment protection.4 Four other Justices signed a concurring opinion by Justice Alito, rejecting the majority’s trespass theory and arguing that the prolonged monitoringof the GPS device constituted a search by violating Jones’s expectation of privacy.5 And finally, Justice Sotomayor both joined the majority opinion and wrote her own concurring opinion, agreeing with the majority that the installation constituted a search but also agreeing with Justice Alito that “‘longer term GPS monitoring in investigations of most offenses impinges on expectations of privacy.’”6

The Jones concurrences, taken together, are potentially a watershed moment in the Court’s Fourth Amendment jurisprudence. Prior to Jones, the Court’s precedent on location tracking—regarding radio “beeper”-based vehicle tracking in the 1980s—indicated that one could have no reasonable expectation of privacy in one’s public movements.7 In Jones, five Justices rejected that proposition, at least with respect to prolonged government surveillance of one’s public movements. Unfortunately, those Justices stopped short of clarifying when one doeshave such an expectation or when surveillance violates it—other than Justice Alito’s conclusion that “the line was surely crossed before the 4-week mark.”8

Trying to make sense of the Jones concurrences and reduce them to a clear and administrable rule—or, alternatively, arguing that they make no sense and cannot be so reduced—has become something of a cottage industry amongst privacy law scholars.9 Building on the work of those who have come before us, this Essay is our attempt to make sense—and “cents”—out of United States v. Jones, by demonstrating how new technologies are continually reducing the cost of surveillance and by attempting to formulate a new approach to defining the Fourth Amendment’s protections based on those falling costs.

Specifically, we propose that a new surveillance technique is likely to violate an expectation of privacy when it eliminates or circumvents a preexisting structural right of privacy and disrupts the equilibrium of power between police and suspects by making it much less expensive for the government to collect information. We explain how courts might put that general proposition into practice by using estimates of the actual costs of particular modes of location tracking to apply a rough rule of thumb: if the new tracking technique is an order of magnitude less expensive than the previous technique, the technique violates expectations of privacy and runs afoul of the Fourth Amendment.

Although we derive this approach from the specific example of location tracking and limit our Essay to that topic, we are hopeful that it may also prove a useful tool in evaluating other surveillance techniques.

I. fourth amendment equilibrium adjustment and the search for metrics of disequilibrium

The courts’ application of the Fourth Amendment is a balancing act, whereby judges tighten or relax the law’s protections in response to changing technology and social norms. When new technologies expand law enforcement’s capabilities, the law does (and should) respond by placing new limits on the government; when new technologies give criminals a leg up, the law does (and should) respond by loosening the government’s reins. At least, that is the gist of the “equilibrium-adjustment” theory of the Fourth Amendment that Professor Orin Kerr recently proposed.10

Professor Paul Ohm characterized Kerr’s equilibrium-adjustment idea as an effective theory for explaining how courts have grappled with a wide range of Fourth Amendment issues over the decades,11 and we agree. Also, at least when it comes to tightening the Fourth Amendment’s restrictions in the face of new tools of government surveillance,12 we agree with Kerr and Ohm that such equilibrium adjustment is normatively desirable.13

We also join Ohm in seeking to “lend rigor” to Kerr’s approach by proposing “hard, objective measures of how much the playing field has tilted”—relevant statistics to guide courts that are trying to measure the impact of a new surveillance technology and decide whether the law should adjust to restore equilibrium.14 Ohm suggests that where a court is weighing police use of a new technology, the police should have to present statistics quantifying the technology’s effect on criminal investigations.15 But beyond making “an admittedly unorthodox proposal”—that “it should take, on average, just as long to solve a crime today as it has in the past”—Ohm stops short of identifying the best statistics to measure, leaving that to future debate and litigation.16

However, by closing with a citation to the theory of Professor Harry Surden, Ohm may point us towards another potential approach for identifying Fourth Amendment disequilibrium: comparison of the cost of acquiring particular evidence with or without the new surveillance technology.17

II. how jones supports the structural privacy rights approach as a model of fourth amendment protection

The theory of “structural privacy rights” that Surden proposes is a simple idea synthesizing several complex ones.18 The simple idea is that structural constraints—physical and technological barriers—make certain conduct costly, sometimes impossibly costly.19 These costs act as non-legal regulations, essentially providing a non-legal “right” against the behaviors they prevent.20 Yet rapid changes in technology can quickly and unexpectedly eliminate these long relied-upon structural rights, especially when it comes to privacy.21 Surden’s message to policymakers, similar to Kerr’s message to the courts, is that they can recognize and adjust for diminishing structural rights against privacy invasion by adding new legal protections to replace them as they are lost—i.e., that they can impose new legal costs to compensate for the drop in actual costs.22

One wonders whether Justice Alito has read Surden’s work, because his opinion in Jones is highly consistent with a cost-centric “structural privacy rights” logic: first noting the structural constraints that would previously have made long-term location tracking impossibly costly and difficult, and then granting Fourth Amendment protection to fill the privacy gap left by GPS tracking technology’s elimination of those constraints.23 After joking that such comprehensive surveillance would have been impossible in the Framers’ era absent “a very tiny constable . . . with [the] incredible fortitude and patience” to hide somewhere in a coach for twenty-eight days,24 Justice Alito explains in terms echoing both Kerr and Surden:

In the pre-computer age, the greatest protections of privacy were neither constitutional nor statutory, but practical. Traditional surveillance for any extended period of time was difficult and costly and therefore rarely undertaken. The surveillance at issue in this case—constant monitoring of the location of a vehicle for four weeks—would have required a large team of agents, multiple vehicles, and perhaps aerial assistance. Only an investigation of unusual importance could have justified such an expenditure of law enforcement resources. Devices like the one used in the present case, however, make long-term monitoring relatively easy and cheap.25

Alito continues:

[R]elatively short-term monitoring of a person’s movements on public streets accords with expectations of privacy that our society has recognized as reasonable. But the use of longer term GPS monitoring in investigations of most offenses impinges on expectations of privacy. For such offenses, society’s expectation has been that law enforcement agents and others would not—and indeed, in the main, simply could not—secretly monitor and catalogue every single movement of an individual’s car for a very long period.26

Justice Sotomayor’s concurrence adopts a similar logic,27 such that all five concurring Justices in Jones seemed to embrace, albeit implicitly, an equilibrium-adjustment approach28—and more specifically, a cost-focused structural privacy rights approach—to resolve the Fourth Amendment question. Indeed, one might nominate this approach as a fifth model of Fourth Amendment protection on top of the four that Kerr has already identified, if only there were a way to systematize and standardize its application.29 But as presented in Jones, the structural privacy rights model is more of a fuzzy principle than a clear and administrable rule.

A central shortcoming of Justice Alito’s opinion is that it hinges on the ever-decreasing cost of prolonged location tracking, but never supports its reasoning with data. It doesn’t specifically describe or compare the cost of prolonged tracking done with and without GPS technology. Nor does the opinion use any data to elaborate on how great a cost difference between prolonged tracking before and after the introduction of GPS technology would justify an equilibrium-adjusting increase in Fourth Amendment protection. If the opinion had “shown its work,” other courts could emulate and apply it. But sadly, as Stephen E. Henderson has noted, Justice Alito’s opinion is “an empirical opinion without any empirics.”30

Those empirics do exist, however, and it is the project of identifying and modeling them to which we turn next.

III. comparing the costs of different location tracking methods

The cost of tracking a suspect’s location has decreased significantly as new technologies have become available to the police. Not all technologies result in the substantial cost savings that would warrant a recalibration of Fourth Amendment law. But some of them, including the dramatic shift in the cost of tailing a suspect before and after the introduction of GPS technology, represent what Surden calls “rights-shifts,” suddenly and irrevocably eliminating a previous structural privacy right.31

This distinction between ordinary technological advances and extraordinary rights-shifts becomes plain in even rudimentary, back-of-the-envelope calculations to estimate and compare the approximate cost of various location tracking techniques. We recognize that different techniques are often used in combination, but for the sake of argument we will estimate the cost of each in isolation. In doing so, we rely on the following assumptions. First, we model our calculations on the circumstances of the Jones case by assuming an investigation staffed by federal agents seeking to conduct continuous and covert surveillance of a vehicle’s movements through urban and suburban environments. Second, our calculations focus only on the cost of acquiring the location information being sought, and do not include the cost of later reviewing it or making investigative use of it. Third, our calculations do not include fixed costs, such as the cost of equipment, as they are amortized over time and over a large number of cases. We only include marginal costs such as personnel costs, operating costs, and other service fees that are specific to an investigation. For example, we do not include the cost of purchasing the car but we do include costs associated with operating the vehicle, such as gasoline. We combine these costs to calculate the total average cost per hour of each type of surveillance for three different time periods of surveillance—one day, seven days, and twenty-eight days as in Jones—to demonstrate the falling cost per hour of certain techniques over time. The cost of some techniques does not vary depending on the length of the investigation, but for those with varying costs, we present a range of values.

We consider the cost of several location surveillance techniques: physical pursuit by foot and in vehicles, as well as location tracking using a radio beeper, a GPS device, or a cell phone.

A. Foot Pursuit

The most basic way to track the location of an individual is to assign an agent to follow that person on foot. An agent can monitor and record an individual’s whereabouts while maintaining some distance to avoid detection. Foot pursuit has clear advantages given that the agent is usually within the line of sight of the suspect and can immediately apprehend the suspect in the act of a crime. Additionally, the agent has the ability to visually confirm that the person he is following is, in fact, the target. However, foot pursuit is constrained by the likelihood that the agent will be recognized as the length of surveillance goes on or that the suspect will give him “the slip” by switching modes of transportation or otherwise evading pursuit.

Regardless of the various pros and cons of foot surveillance, our main concern is with its cost as a means of acquiring location information. In our model, the primary cost of foot pursuit is the salary of the agent. An FBI agent’s salary32 plus benefits33 and availability pay34 is approximately $130,962 per year, assuming an agent of average experience.35 Agents are required, “to average a 50-hour work week over the course of the year.”36 So, given 2,600 “working hours” in a standard calendar year, we estimate the hourly “pay cost” for an FBI agent to conduct surveillance on foot to be $50 per hour. We therefore consider this the “base unit” cost for a law enforcement agent engaged in surveillance.

B. Covert Foot Pursuit with Five Agents

Law enforcement typically uses a technique known as a “surveillance box” to overcome the limitations of single-agent pursuit and successfully conduct longer-term covert surveillance.37 This approach stations multiple agents—in our example, five38—around a target in such a way that, no matter which way the target travels, one agent will have a clear path to follow. This allows the agents to monitor the subject without interruption, even if the target exhibits unexpected behavior, by allowing agents to “hand off” the task between one another when necessary to change shifts or take a break. Assuming a five-agent box at a cost of $50 each per agent-hour, we arrive at an hourly cost of $250 for continuous covert surveillance.

C. Single Car Pursuit

Law enforcement can also track a suspect from a vehicle, typically using two agents per vehicle.39 However, single-vehicle pursuit suffers from many of the same limitations as single-agent foot pursuit, and also adds vehicle operating costs such as fuel. We estimated the hourly cost of the car using the Internal Revenue Service’s standard deduction, assuming an average speed of thirty-five miles per hour and assuming that the suspect will be in motion about twenty-five percent of the time.40 The additional cost of using a vehicle to pursue a suspect is relatively low—the bulk of the cost in both of these cases is from personnel and not technology expenses. We combined those expenses to arrive at an approximate average cost of $105 per hour.

D. Covert Car Pursuit with Five Cars

As with foot pursuit, the problems of single-vehicle pursuit are typically overcome by using a surveillance box. This method “consists of positioning surveillance vehicles in such a manner as to control routes of travel out of a specified area.”41 So, if the target is on a city grid, a surveillance team would need five vehicles to cover all possible movements—one for each direction and another able to move ahead of the team in case the target makes an unexpected move and the box has to shift to catch up.

Assuming one agent per car and five cars, with each agent costing $50 per hour, gives us a base personnel cost of $250, to which we add $25 in operating costs for all five cars using the same hourly cost of $5 per car that we calculated for single-car pursuit. We thus arrive at $275 as the total hourly cost of covert car pursuit.

Figure 1.

a surveillance box established for covert pursuit of target through city streets

E. One Car Covert Pursuit Using “Beeper” Technology

Agents in a vehicle can also track a suspect using a radio-based “beeper” device that sends a signal received by an antenna on the agent’s vehicle.42 This signal can indicate the direction of the transmitter’s location from a distance of two to four miles.43 Law enforcement agents can attach the transmitter to a suspect’s vehicle or surreptitiously place it on an object that will travel with the suspect.44 Beepers are cheap to operate once the equipment has been purchased, requiring only two agents: one to drive and one to make any necessary adjustments to the receiver during pursuit.45

The hourly cost will vary depending on the length of the investigation, because the initial installation costs will be amortized over time.46 We are conservatively estimating that it takes an agent a full hour to install and another hour to remove a device attached directly to the vehicle’s electrical system, with another agent keeping a look out, totaling four hours for each investigation, regardless of length. So, if the agents follow a target for only one day, beeper technology costs $113 per hour, but if the investigation continues for twenty-eight days the hourly cost falls to $105.

F. Cell Phone Tracking Using an IMSI Catcher or “Stingray”

Rather than pursue a suspect directly or by using beeper technology, law enforcement agents can track the location of a target’s cell phone by using a device—known as an IMSI Catcher or “Stingray”—that simulates a cell tower in order to collect information about the location of nearby cell phones.47

Agents use Stingrays in a manner similar to their use of beepers, and with the exception of the attachment-related costs, the cost of using an IMSI catcher for surveillance is essentially the same as using a beeper. Therefore, putting aside the up-front cost of the IMSI catcher itself, the only costs for IMSI catcher surveillance are the cost of the agent operating the device, the cost of the agent driving the pursuit vehicle containing the device, and the operating costs of that vehicle.

G. Tracking Using a GPS Device

A recent survey of over seventy law enforcement agencies demonstrates how new technologies are transforming policing: eighty-three percent of the respondents to the survey “use Global Positioning System technology (GPS) to track the movements of criminal suspects.”48 Clearly, GPS-based vehicle tracking is an incredibly popular alternative to foot, car, or beeper-based pursuit.

Although there are different types of GPS devices, we will focus on the devices that are powered directly from the vehicle’s battery.49 These devices require less upkeep, but are more difficult to install because they require an agent to get access to a vehicle’s electrical system. As with beeper technology, we conservatively estimate that this technology takes one hour to install and one hour to remove, with one agent doing the work and another agent looking out. Also as with the beeper, these fixed installation and removal costs result in a range of hourly costs depending on the length of the investigation.

In addition to the personnel costs incurred by installing and uninstalling, there is a monthly service fee associated with GPS devices. Tracking with a GPS system requires access not only to the device itself, but also to the network receiving the data the device collects about the target’s location. There are private companies that provide service contracts similar to a consumer cell phone contract with a fixed cost for the device and a fee for its use. We calculated the hourly cost of GPS tracking based on the monthly fees associated with products offered by LiveViewGPS, a company that sells GPS tracking equipment to law enforcement.50 The monthly service fee for its hard-wired GPS products is approximately $40 per month.51

Combining these costs—the per-month fee plus two hours of salary for each of two agents to install and uninstall the device—the total cost of surveillance using a GPS device would be $240 per month. That comes out to $10 per hour over one day, $1.43 per hour over seven days, and $0.36 per hour over twenty-eight days.

H. Cell Phone Tracking with Carrier Assistance

Rather than pursue a suspect in the field, law enforcement agents can track subjects by following the signal of their cell phones by obtaining location information from the provider.52Cell phone carriers have the ability to provide reliable data on the location of a phone at any minute with a reasonable degree of accuracy, often down to a particular city block.53

Data gathered by the American Civil Liberties Union (ACLU) show that cell phone companies will provide location data to law enforcements at varying rates. As of August 2009, “Sprint charges $30 per month per target to use its L-Site program for location tracking. AT&T’s E911 tool costs $100 to activate and then $25 a day. T-Mobile charges a much pricier $100 per day.”54 We used this data to develop an hourly rate for each company, and we present the minimum and maximum charges as the range of hourly costs law enforcement might expect to pay for this method of surveillance. Our calculations include any fees charged to initialize the process (when applicable) because they are specific to an investigation, but those costs are included in the hourly rate.

Given the downward trajectory of technological costs, the increased automation of these services via self-service web portals, and the fact that reimbursement to carriers is limited to reasonable, directly incurred costs,55 we might expect that these rates will decline further over time.

Table 1.

average costs of different location tracking methods

IV. a mathematical formula for reasonable expectations of privacy?

The Jones concurrences, read in the context of Surden’s structural privacy rights model and the Kerr/Ohm dialogue about equilibrium and metrics, point to a new but still somewhat fuzzy rule: If a new surveillance technique eliminates a previous structural right of privacy by making it extremely inexpensive for the government to collect information that otherwise would have been impossible or prohibitively costly to obtain, the use of that technique violates an expectation of privacy. Such a rule would effectively use the Fourth Amendment to impose new legal costs to replace a lost structural right and thereby restore equilibrium.56

Sensibly applying such a rule requires data, and the data we’ve collected demonstrate some basic facts about the costs of location tracking. The data support Justice Alito’s conclusion that following covertly on foot and by car—which cost roughly the same—are very expensive endeavors requiring a lot of manpower.57 Following covertly using a beeper or an IMSI catcher is significantly but not radically less expensive because, although it reduces the number of agents necessary from five to two, it does not eliminate the need for agents to be on duty throughout the surveillance. The cost of GPS-based tracking does radically reduce the cost, however, because it reduces the manpower needed to just the few hours necessary to install and uninstall the device. Carrier-assisted cell phone tracking reduces costs even more so by eliminating the need for installation, bringing the costs to as low as $30 total to monitor a suspect for an entire month.

Focusing on the examples most relevant to the Karo (beeper), Knotts (beeper) and Jones (GPS device) precedents, we find that the total cost of using one car and a beeper over a twenty-eight-day period is nearly three hundred times the cost of doing the same tracking using a GPS device. The difference between GPS tracking and traditional five-car pursuit is even more dramatic: the total cost of using the cars is nearly 775 times more expensive than the cost of using GPS. In contrast, the difference in the cost of beeper surveillance and covert car pursuit without a beeper is significant but well within the same order of magnitude: twenty-eight days of covert car pursuit is only about 2.5 times the cost of beeper-assisted surveillance.

Relying on the surveillance costs involved in these precedents, we arrive at a rough rule of thumb:If the cost of the surveillance using the new technique is an order of magnitude (ten times) less than the cost of the surveillance without using the new technique, then the new technique violates a reasonable expectation of privacy.

Consistent with the Jones concurrences, this approach follows a structural privacy rights model, likeSurden’s, and seeks equilibrium, as Kerr suggests. Unlike the concurrences, however, it provides a clear, objective metric for determining when a previously existing structural right has been lost. Has the new technique reduced costs by a factor of ten or more? If so, a rights-shift has occurred and the Fourth Amendment must be used to impose new legal costs and restore balance.58 Drawing the line at an order of magnitude is admittedly somewhat arbitrary, but is also an indisputable benchmark and easily applicable test for whether or not a particular type of surveillance has become radically less expensive, which is ultimately the question on which we are suggesting courts focus.

This test provides an objective metric, as Ohm suggests,59 but is both easier to derive and more specific to the particular case and technology at hand than the more general metrics he proposes. This test also addresses one of the primary criticisms of Justice Alito’s approach: that it rests on the subjective expectations of people who lack any reliable knowledge about the possibility, likelihood, or capabilities of the particular surveillance techniques being used. As Kerr has argued, “Some people will guess that privacy invasions are common. Others will guess that they are rare. But exceedingly few will know the truth, which makes such probabilistic beliefs a poor basis for Fourth Amendment regulation.”60This test, however, doesn’t rely on anyone’s subjective expectations but only on objective, verifiable facts.

Just as importantly, this rule makes sense of the Supreme Court’s differential treatment between the beeper tracking in Karo and Knotts and the GPS tracking in Jones. The more than fifty percent decrease in the per-hour cost between covert car pursuit ($275) and beeper tracking ($105-113) was large, but not large enough to require an equilibrium adjustment.61 However, GPS tracking ($0.36-$10) is more than ten times less expensive than beeper tracking ($105-$113), clearly triggering the rule.

Similarly, the incredibly inexpensive technique of cell phone tracking clearly requires an equilibrium-adjusting application of Fourth Amendment protections for any length of surveillance. This conclusion is clear when comparing traditional covert car pursuit or beeper surveillance to even the most expensive hourly rate for cell phone tracking using the most expensive cell phone carrier. It costs $5.21 per hour for one day of surveillance of an AT&T customer. One day of beeper surveillance is more than twenty times as expensive, at as much as $113 per hour, and covert car pursuit costs over fifty times that, at $275 per hour.

The difference is even more dramatic when the length of the surveillance increases. For example, the average cost of cell phone tracking across the three major providers is about $1.80 per hour for twenty-eight days of tracking. Using beeper technology for the same period of time is nearly sixty times more expensive, while covert car pursuit is over 150 times more expensive.

Speaking more generally, any technology used for mass location surveillance would trigger our rule, because as the number of targets increases, the cost of tracking each one approaches zero. This result accords with the Court’s suggestion in Knotts that technologies enabling “dragnet-type law enforcement,” whereby “twenty-four hour surveillance of any citizen of this country [would] be possible,” may justify the application of “different constitutional principles” than the garden-variety single-target tracking case does.62 Judge Posner subsequently made the same point when discussing GPS tracking:

The new technologies enable, as the old (because of expense) do not, wholesale surveillance. . . . It would be premature to rule that such a program of mass surveillance [of public movements] could not possibly raise a question under the Fourth Amendment—that it could not be a search because it would merely be an efficient alternative to hiring another 10 million police officers to tail every vehicle on the nation’s roads.63

Rather than reserving judgment on the question, our rule asks and answers it: mass surveillance technologies, by reducing the cost of tracking any citizen to pennies or less per day, require imposition of Fourth Amendment constraints as a legal prophylactic to replace lost structural constraints. Put another way, our rule concludes that mass-tracking technology implicates the Fourth Amendment exactly because it is an efficient alternative to the (impossibly costly) hiring of another ten million police officers.

Figure 2.

a visual comparison of location tracking methods

This chart compares the cost of each method of tracking a suspect’s location, using the most expensive possible per-hour cost for each method. Even when using the most costly rate—for example, $10 per hour for GPS tracking or $5.21 per hour for cell phone tracking—the drop in cost between old and new techniques is very dramatic and well over an order of magnitude.

This conclusion can be illustrated by a simple example. The FBI has stated that in response to the Jones ruling, it had to either get warrants for, or deactivate, the 3,000 GPS devices that were deployed at that time across the United States.64 This implies that the Bureau had the technical capacity to covertly follow at least 3,000 targets simultaneously using GPS technology. Without that technology, it would require 15,000 agents to covertly follow the same number of targets (assuming five agents for each target). Therefore, even if the FBI were to instruct all of its 13,785 special agents65 to ignore all other duties and remain active for every hour of every day (an assignment that is humanly impossible), it would still be 1,215 agents short of being able to follow that many suspects. These figures dramatically illustrate how mass surveillance that was impossible prior to the introduction of new technologies like GPS is now firmly within the government’s grasp. When such surveillance would have required ludicrous expenditures of time and treasure, there was no need for the Fourth Amendment to protect against it. However, now that the structural constraints against that surveillance have disappeared and the absolutely impossible has become easily possible, Fourth Amendment protection is desperately necessary.

This view is not only consistent with that of several scholars who have interpreted the Jones concurrences to support a rule restricting mass surveillance,66 but is also consistent with the concerns expressed by the Justices themselves during the Jones oral argument. As Justice Breyer put it:

[T]he question that I think people are driving at, at least as I understand them and certainly share the concern, is that if you win this case, then there is nothing to prevent the police or the government from monitoring 24 hours a day the public movement of every citizen of the United States.67

The Chief Justice put an even finer point on it: “You think there would also not be a search if you put a GPS device on all of our cars,monitored our movements for a month? You think you’re entitled to do that under your theory?”68

Ultimately, several Justices posed questions raising the concern that a failure to regulate GPS tracking could enable mass or indiscriminate warrantless surveillance.69 And although the Jones concurrences themselves do not explicitly discuss the issue of mass surveillance, the structural rights calculus that these opinions support clearly implicates that question and provides an answer: where technology renders previously impossible surveillance possible on a mass scale, the Fourth Amendment must be applied to restore equilibrium.

Conclusion

This Essay set out to make a targeted contribution to an ongoing conversation about how the Fourth Amendment’s protections can and should be applied to balance out the rapid technology-based expansion of the government’s power to collect information about its citizens. Our contribution is the suggestion that dollar cost can be a key metric for judging when such a radical shift in police power has occurred. With location tracking as our example, we’ve detailed the precipitous drop in cost between old and new surveillance techniques, and, consistent with previous academic discussions and the Jones concurrences, we have suggested ways in which such data about costs could be used to apply a simple and administrable rule.

We do not argue that the courts should abandon the reasonable expectation of privacy as the primary test for Fourth Amendment protection, but instead propose a supplementary new tool for deciding when such an expectation exists in cases concerning new surveillance technologies. Nor do we suggest that the cost metric can or should be the only factor in making that decision; we only seek to demonstrate its viability as a powerful yardstick against which to judge a technology’s impact on privacy. As such, using order-of-magnitude difference as a rule of thumb is just one way of using cost as a metric, and we welcome other such proposals for assessing whether a radical technology-prompted rights-shift has occurred.

We also recognize that even our simple rule of thumb raises some questions about implementation and administrability. The assumptions that inform our calculations can and should be questioned, as there may be more accurate ways of assessing shifts in surveillance costs, and we welcome suggestions and further research on this point. Like Ohm, we imagine that if our approach is ever embraced, the exact nature of the cost calculus, and what data should be used for it, will be the subject of much debate and litigation.70 For now, our modest hope is to inspire an enterprising criminal defense attorney to articulate cost-based arguments when moving to suppress GPS or cell tracking data. Our less modest hope is to see that motion granted.

Finally, there remains work to be done in assessing how such a cost-based structural privacy rights approach might apply beyond the immediate example of location tracking—for example, in the context of drone surveillance, communications surveillance, or data mining. That work is beyond the scope of this Essay, though we expect it would yield both new insights for and new challenges to our basic proposition: When highly revealing surveillance of a citizen’s activities is possible for pennies a day, we need the Fourth Amendment to protect us. Otherwise, we may soon live in a world of unlimited virtual “tiny constables” monitoring our every move.

Kevin Bankston is Policy Director of the New America Foundation’s Open Technology Institute, though the views expressed here are his own. Ashkan Soltani is an independent researcher and consultant specializing in consumer privacy and security. The idea for this paper originated as a presentation on “The Cost of Surveillance” by Ashkan Soltani at the Security and Human Behavior conference in 2012. A draft of this article was presented at the 2013 Privacy Law Scholars Conference and benefited very much from the comments received there. The authors are especially grateful to Alvaro Bedoya, Matt Blaze, Michael German, Orin Kerr, Caren Morrison, Deirdre Mulligan, Paul Ohm, Amie Stepanovich, Bruce Schneier, Harry Surden, and Peter Swire for their feedback and encouragement, and to Gautam Hans and Alethea Lange for their extensive editorial and research assistance.

Preferred citation: Kevin S. Bankston & Ashkan Soltani, Tiny Constables and the Cost of Surveillance: Making Cents Out of United States v. Jones, 123 Yale L.J. Online 335 (2014), http://yalelawjournal.org/forum/tiny-constables-and-the-cost-of-surveillance-making-cents-out-of-united-states-v-jones.