Introduction: Widely Distributed Detection Systems (WDDSs)
On July 21, 2007, as part of a controlled experiment, a twenty-six year old male smuggled a source of radioactive Co-60 onto the campus of Purdue University in West Lafayette, Indiana. The Co-60 source, stored in the subject’s backpack, was a radioactive isotope that could form the core of a radiological dispersal device, popularly known as a “dirty bomb.” Undetected, the subject concealed the backpack in a parking lot adjacent to a high-rise building in Purdue’s engineering complex.
Fifteen minutes later, the Indiana Department of Transportation (INDOT) was tipped to the presence of radioactive nuclear material on Purdue’s campus. INDOT deployed a team of agents to locate and recover the material, each equipped with a gamma-ray detection sensor attached to a cell phone. The cell phones were networked with a server that had previously analyzed gamma-ray detection data from Purdue’s campus to calculate a local radiation baseline.
As the INDOT team fanned across Purdue’s campus, the agents’ cell phones sent digital packets conveying the detected gamma-ray counts to the computer server. Patented image processing software run by the server projected a visual map that displayed in real time the deviation between the gamma-ray levels detected at each agent’s location and the previously determined radiation baseline. Within five minutes, the agents detected significantly elevated gamma ray levels. Two minutes later the team located the backpack, and safely secured the nuclear material. The whole INDOT operation lasted twelve minutes.
The success of this experiment heralds a new mode of intelligence collection in which data acquired jointly by government and non-government actors is aggregated and analyzed to swiftly locate a weaponized substance. This collection is enabled by means of a “widely distributed detection system” (WDDS), a term I coin to refer to an integrated network of individual devices with three features: (1) portable detectors capable of identifying and reporting the presence of hazardous nuclear, chemical, or biological material, (2) a central server that correlates real-time readings against historical baseline data to distinguish true threats from false positives, and (3) image processing technology that triangulates verified threat data to pinpoint the location of an illicit substance.
Much of this technology exists. Physicists at Purdue University have developed a WDDS utilizing cell phones equipped with inexpensive gamma-ray sensors to detect nuclear radiation. Notably, the correlation capability and image processing software patented as part of the Purdue WDDS is not limited to nuclear detection, but could be adapted to analyze samples of chemical or biological material. The most formidable hurdle that remains is engineering a portable sensor to detect weaponized chemical and biological agents. However, recent innovations in portable DNA sequencing and mass spectrometry portend the near-term prospect of cell phone-enabled biological and chemical analyses that could support a WDDS. A miniature DNA sequencer that plugs into a USB drive and generates real-time data is commercially available and widely used, and its manufacturer has announced a mobile-phone-based successor. Newly innovated handheld mass spectrometers use a vacuum to sample ions directly from the air and provide chemical analyses in real time. Smaller and more portable mass spectrometers could be developed in the near future, but even current models can be affixed to vehicles with adequate space and power capacity, including buses, fire trucks, ambulances, and many cars.
This Article discusses the promise of WDDSs from the perspective of the American intelligence community (IC). First, I outline the technical and legal ways in which networked portable detection can augment existing intelligence capabilities and substantially diminish the threat of a WMD attack in America, particularly in densely populated areas targeted by hostile actors. Second, I illustrate how the government can nest WDDSs within legal and policy frameworks that protect the privacy and dignity of WDDS participants, and establish a blueprint for reconfiguring the IC’s strained relationships with the American public, building the foundation for future collaborations.
I. The Intelligence Advantages of WDDSs
As collection platforms, WDDSs are compelling because they excel in precisely the areas where traditional intelligence tools are least effective. First, the performance of a WDDS is optimized in regions of high population density—target rich environments for terrorists where intelligence leads can be difficult to operationalize. As the number of devices increases in a specific location, the cumulative data reported before an incident produces a more accurate baseline measurement, which then diminishes the probability of registering a false positive in that area. Should terrorists subsequently attempt to carry nuclear, chemical or biological material through congested space, the numerous portable detectors in proximity to the weapon would quickly alert the WDDS to the presence of the material and its location. Indeed, a well-subscribed WDDS would presumably deter hostile actors from even attempting to smuggle weaponized materials through populated areas, allowing the government to allocate additional resources to monitoring more remote targets. Though the precision and accuracy of detectors will improve over time, the sheer number of measurements reported in populated areas can statistically overcome minor errors in individual readings, such that WDDSs can function effectively even as detection technology continues to advance.
Second, WDDSs are uniquely capable of disrupting lone actor attacks and other homeland threats that are challenging for the government to track using traditional intelligence methods. In theory, a sophisticated syndicate could design and transport a WMD that leaves a light “physical trail” by minimizing the emission of trace substances. While such a weapon might be more difficult for a WDDS to identify, the effort to develop the WMD could create a significant “social trail” for the government to monitor—perhaps through communications among co-conspirators, money transfers, the sale and transport of component materials, or the travel of known weapons experts. An attempted WMD attack by a lone actor may leave a comparatively light or indiscernible social trail, but a device configured without the aforementioned resources would likely generate a physical trail that could easily be identified by a WDDS, even in sparsely populated regions. Thus the comparative advantage of WDDSs in detecting physical trails nicely complements the IC’s existing capability to monitor social trails; most plausible attack strategies would leave clues of one type or the other.
Third, WDDSs offer unique intelligence advantages in the immediate aftermath of an event. Though the primary objective of intelligence is to disrupt attacks before they occur, accurate intelligence in the seconds, minutes, and hours after a WMD attack can substantially reduce injuries and casualties by enabling first responders to identify and evacuate the zone of danger, and direct first aid to the subset of endangered individuals actually impacted by the attack. In a WMD attack, the dispersal of weaponized nuclear, chemical or biological agents would not be linear, uniform, or easily modeled, but would vary according to numerous factors that would be extraordinarily difficult to predict. Traditional intelligence and law enforcement tools are designed to prevent mass casualty events, and lack the breadth or granularity to produce person-level impact data after an attack occurs. But WDDSs offer exactly these capabilities. Anyone carrying or transporting a personal detector in close proximity to an attack would report contemporaneous data that not only reflects the fact of their exposure to a toxic substance, but also quantifies the level of exposure. Collectively, data reported from the attack zone would reveal the origin of the event and the vectors of the substance released in the attack, thereby enabling informed first responders to divert people away from the known and projected dispersal path.
Finally, WDDSs allow the government to process information it probably could not collect unilaterally under the Fourth Amendment. Though the government enjoys some latitude to acquire environmental data in public places without a warrant, the Supreme Court has expressed discomfort with warrantless monitoring of public areas that is pervasive or lengthy in duration. In circumstances where the government identifies a prospective WMD threat but lacks probable cause to obtain a surveillance warrant, localized WDDS data reported voluntarily by private subscribers could fill an intelligence gap that might otherwise preclude the government from tracking a nascent but potentially dangerous subject. Far from an end-run around the Fourth Amendment, WDDSs embody the principle that when private parties willingly provide information to the government, the government’s use of that information does not offend the Constitution.
II. Building Public Support for WDDSs
In most contexts it would be foolish to ask individuals to voluntarily adopt a technology that enables the IC to access a continuing stream of data from their personal devices. Yet WDDSs offer a plausible argument for pioneering this novel and desirable arrangement. First, society does not recognize a fundamental right to conceal weaponized nuclear, biological or chemical material from the government. Configured properly, a WDDS would only record the levels of highly toxic nuclear, biological or chemical substances in a specific location at a particular time. Since little if any legitimate behavior is exposed by this data, the government’s acquisition and use of WDDS data would not chill the exercise of constitutionally protected freedoms.
Nor is it far-fetched to envision communities promoting WDDSs to local residents, particularly in areas that hostile actors are likely to target. A variety of personal motivations could catalyze grassroots support for WDDSs, including patriotism, civic responsibility, peace of mind, or even the economic benefit of owning property or operating a business in a locality secured by a reputably well-subscribed WDDS.
Finally, individuals could conclude that participating in a WDDS is in their self-interest. In the event of a nuclear, biological, or chemical attack, people in the vicinity of the attack with access to a networked portable detector will know definitively whether they have been exposed to radiation or a toxic substance, and their level of exposure. Even if the risk of an event is low, WDDSs provide comfort by reducing the likelihood of injury or emotional anguish resulting from insufficient information after an attack. Notably, the cost of participating in a WDDS—providing personal information to the government—is a price people routinely pay to enhance their probability of surviving an unforeseen event. Indeed, many individuals with diabetes, epilepsy, or uncommon food and drug allergies wear medical alert bracelets that disclose sensitive health information to first responders who may need to render assistance. The intrusion from conveying non-biographic location and environmental data to the government is mild by comparison.
Notwithstanding these benefits, the prospect of using WDDSs to collect and aggregate environmental data evokes two serious misgivings. First, any technology used to link a personal device to a government server presents, at least in theory, a means for the government to obtain other information stored on, accessible through, or collected by that device. As the Supreme Court has observed, “[t]he sum of an individual’s private life” can be reconstructed through data procured from a cell phone. Aside from information about the user, many personal devices have superior audio and video recording capabilities that can be used to monitor legitimate, constitutionally-protected activity that occurs within range of the device’s microphone or camera.
Second, as the government’s missions and surveillance tools evolve, many fear that advancing technology coupled with a heightened threat environment will inexorably lead to an omniscient monitoring capability that eliminates privacy in American society. From this perspective, even if a WDDS reports innocuous information that serves an important security purpose, any program that dramatically increases the volume of data gathered by the IC hastens the onset of a dystopia in which the government is irrevocably tangled in the private lives of its citizens.
These concerns are not a critique of WDDSs per se, but reflect deep-seated doubts about the IC’s capacity to self-regulate, honor boundaries, and tolerate reasonable risk in the service of cherished democratic values. To overcome these apprehensions and build the trust required for WDDSs to succeed, the IC must exercise three new muscle movements antithetical to the current culture of intelligence collection. First, the IC must formulate a legal framework for WDDSs that imposes ironclad constraints on the exploitation of WDDS data, and deputizes private actors to help enforce those requirements. Second, the IC must dispel its perceived ambition to terminally encroach on Americans’ privacy by enacting policies that not only clarify the limits of the government’s intelligence authorities, but go further to affirmatively demarcate the zone of activity where Americans can conduct their lives without fear of being surveilled. Finally, the IC must sustain an open dialogue with private constituencies through an outreach program that solicits and addresses public critique of the status quo. Each proposal is discussed below.
These challenges are daunting, but they present a golden opportunity for the IC to overcome the public’s current misgivings about domestic information gathering in a context where Americans would be favorably inclined to seek the security advantages of collaborating with the government. The success of this endeavor could transcend the emergence of WDDSs as a critical security shield, and allow the IC to reap substantial benefits from a generally improved relationship with the public.
A. A New Legal Approach to Accommodate Collaborative Intelligence Gathering
Until now, the IC has equated effective intelligence gathering with secrecy and obscurity. The legal framework initially developed to regulate intelligence collection was moored to an ideal of intelligence activity as a unitary executive branch function with minimal public profile. Over time, the IC has retreated from this standard in response to external pressure for increased accountability, or the need to engage other branches of government. For example, the intelligence abuses reported by the Church and Pike Committees in 1978 impelled Congress to enact the Foreign Intelligence Surveillance Act (FISA) in order to regulate electronic surveillance conducted in the United States. However, the IC continued to resist congressional involvement in overseas intelligence collection until the late 2000s, when it asked Congress for a more efficient legal process to compel the private assistance required to intercept overseas communications traversing domestic telecommunications infrastructure (resulting in the FISA Section 702 program).
Today’s IC is unquestionably more transparent than its predecessors. However, over the last four decades this change has been incremental, not transformative. The IC typically regards calls for increased oversight and accountability as potential losses to be minimized—not as a transactional exchange with the public that could yield operational benefits.
In hindsight, the legal structure erected to fortify the IC against public exposure has not always served the government well. The unauthorized Snowden disclosures in 2013 demonstrated that discrepancies between perception and reality in the realm of intelligence activity can lead to undesirable outcomes—there, policymakers compelled the IC to undertake reforms, but IC elements earned no commensurate credit or trust with the public by successfully meeting these new obligations. Widespread concern that the Snowden leaks have eroded the norm of classified information remaining secret should reinvigorate the discussion of whether additional investments in transparency can mitigate the impact of subsequent leaks and rehabilitate the IC’s relationship with the public.
If these conditions empower the IC to barter a measure of secrecy for the efficacy offered by a collaborative intelligence venture, the legal protections required to spur public participation in WDDSs should be feasible for the government to implement. As illustrated by criticism of the former Section 215 bulk telephony metadata program and the recent debate over the reauthorization of FISA Section 702, the public’s comfort with intelligence collection appears to be a function of four factors. The first factor is whether the collection program is confined to the executive branch or regulated by multiple branches. The debate over Section 702 reauthorization reflected that while privacy and civil liberties groups contest certain elements of the Section 702 program, they at least implicitly acknowledge the benefits that should accrue from the congressional regulation and judicial review mandated by the FISA Amendments Act. Significantly, discussions surrounding the Section 702 reauthorization process led commentators to propose similar reforms to executive branch collection programs that lack analogous oversight or judicial safeguards, noting that these programs engender less trust and support outside government.
The second factor concerns who holds the data. Negative reaction to the revelation that the government acquired bulk telephony metadata under Section 215 of the USA Patriot Act induced Congress to replace the bulk metadata program with a more politically palatable regime in which private phone providers retain exclusive custody of telephony metadata, permitting government searches only pursuant to particularized orders from the Foreign Intelligence Surveillance Court. Rational or not, the demise of Section 215 bulk collection underscores the reality that private companies are still seen as more trustworthy stewards of personal information than government agencies; it is hard to envision private parties voluntarily transmitting sensitive information to repositories accessible only to government personnel.
The third factor is whether the government must obtain consent to collect an individual’s personal information. With relatively little scrutiny the IC obtains information that individuals voluntarily provide to government agencies to receive many entitlements and services, including passports and visas, government benefits, and access to the financial system. Though it may be impractical to withhold this information from the government, collection programs acquiring only voluntarily disclosed information better empower individuals to manage their profile with the government and limit the risk that personal information in the government’s custody will be used to undermine the subject’s liberty or welfare.
Finally, there is the question of whether the government can use consensually collected information against the subject in criminal proceedings. Controlling exposure to the criminal justice system is a paramount concern of IC critics. While the Fourth Amendment significantly restricts the government’s acquisition of non-public information for law enforcement purposes, it affords fewer protections to information the government acquires consensually or pursuant to its foreign intelligence authorities. Hence, one of the most controversial elements of the Section 702 program is the government’s use of United States person information incidentally acquired without a warrant to support law enforcement activity. Ultimately, WDDSs are unlikely to attract public support if individuals can incriminate themselves by voluntarily reporting detection data to the government.
Collectively, this analysis suggests a viable legal framework for WDDSs. To maximize the appeal of WDDSs, the IC should propose that Congress enact a statute to create and fund the WDDS infrastructure. This statute would legislate congressional oversight of WDDSs, and require that WDDSs host information in repositories that are maintained by private entities and accessible only to a limited group of trained government operators. The operation of this program would be regularly audited by a panel of overseers representing the government, private industry, and civil liberties organizations.
The panel would oversee compliance with four specific requirements. First, the government would be permitted to collect information only from individuals “opting in” to a WDDS, and subscribers could discontinue their participation at any time. Second, WDDSs would only collect a device’s geographic coordinates and detection readings; the law would expressly prohibit WDDSs from gathering any additional content, or any metadata identifying the reporting device. Third, the government would be barred from using detection reports to incriminate the person transmitting the data to the WDDS. Since anyone transporting WMD material would induce devices nearby to report the illicit substance, in practice this requirement would not hinder the government from prosecuting the perpetrator of a WMD attack using evidence gathered from other networked devices in the vicinity of the weapon. Finally, the panel would audit and investigate false positives generated by a WDDS in order to minimize government searches or seizures prompted by inaccurate reports.
B. Increasing Comfort with WDDSs through Strategic Policy Compromise
Viewed in isolation, WDDSs operating within the legal constraints outlined above would minimally intrude on a participant’s privacy. Yet the public is unlikely to support WDDSs if the government’s acquisition of detection data could undermine civil liberties by amplifying in unpredictable ways the government’s existing surveillance capabilities. Unfortunately, the public is not well positioned to assess the marginal impact of WDDSs, because the IC has never meaningfully delineated the substantive parameters of its intelligence activities. While the IC’s surveillance authorities are bounded by the definition of foreign intelligence in FISA and Executive Order 12333, these definitions are so broad that to a lay member of the public they rule nothing out.
Among the three primary attributes of intelligence collection—what is collected, how it is collected, and who is targeted—the importance of protecting the “how” and the “who” is intuitive and easy to justify, but ambiguity surrounding the “what” has less obvious tactical advantages, and profound social consequences. The government acknowledges in other contexts that members of vulnerable minority groups, or organizations that coalesce around unpopular viewpoints or lifestyles, are susceptible to the fear that broadly scoped intelligence authorities threaten their personal privacy and the integrity of their community. These anxieties can chill the exercise of constitutional rights and freedoms and diminish the quality of life for many segments of the population that the IC must win over to develop a viable WDDS capability. On the other hand, there is little evidence to suggest that a narrower and more precise articulation of the threats that drive intelligence collection would reduce the utility of the government’s surveillance authorities. Indeed, criminal wiretaps remain an effective law enforcement tool, even though the illicit activity that activates these authorities must be criminalized through laws crafted “with sufficient definiteness that ordinary people can understand what conduct is prohibited and in a manner that does not encourage arbitrary and discriminatory enforcement.”
In 2014, President Obama issued Presidential Policy Directive 28 (“PPD-28”), a declaration of the objectives, principles and limitations governing the United States’ signals intelligence collection activities overseas. PPD-28 is intended to reassure foreign governments, companies and citizens that the United States’ acquisition of overseas communications is not boundless or undisciplined, but reasonably calibrated to advance America’s national security interests without capriciously violating the privacy of foreign entities lacking constitutional rights or procedural recourse in America’s courts. It provides, in relevant part, that “[s]ignals intelligence shall be collected exclusively where there is a foreign intelligence or counterintelligence purpose to support national and department missions and not for any other purposes.”
Though this excerpted language characterizes the United States’ national security mission at a high level of generality, as a whole, PPD-28 provides an apt framework for codifying strategic policy concessions to encourage participation in WDDSs. In essence, these concessions should restrict the availability of intrusive intelligence methods in circumstances where the use of surveillance tools may technically be legal, but their impact would be too corrosive to justify the expected intelligence gains. The ideal vehicle for these concessions is a new executive order or policy directive that parses the expansive definition of foreign intelligence in FISA and Executive Order 12333, and enumerates the protected activities and behaviors that fall either outside this definition or beyond the new policy limits promulgated by the President. Executed properly, this proclamation would reassure members of vulnerable communities that they will not be surveilled absent a strong, documented connection to a serious threat.
C. Promoting WDDSs through Direct and Sustained Public Outreach
Even in an optimized legal and policy climate, the IC will need to successfully market WDDSs to parties outside the government, including minority groups and privacy advocates. Historically the IC has shown little enthusiasm for directly engaging the public, and lacks the outreach capability deployed by agencies in other sectors where public support is a more prized commodity. Perhaps this reticence reflects an assumption that the differences between intelligence agencies and privacy advocates are so foundational that outreach is unlikely to reveal common ground or produce tangible results. The IC might also resist public exchanges on intelligence matters because relevant information is often classified or sensitive, and counterparts may not be incentivized to handle such information with discretion.
What scant dialogue exists between the IC and the public is brokered by the Civil Liberties Privacy Officers (CLPOs) at IC components. CLPOs are tasked with ensuring that IC components comply with the civil liberties and privacy protections codified in existing laws, regulations and policies. This approach misses the point. Public apprehension toward the IC is driven less by the IC’s failure to meet its current obligations than by a perception that those obligations are themselves insufficient. CLPOs removed from the operational activity at their components and positioned outside the decisional chain of command have limited means of instigating the change the public may demand as a condition of supporting WDDSs.
WDDSs alter the IC’s outreach calculation by reconceiving the public as a resource to develop, rather than an adversary to placate. This new dynamic mitigates the concerns that generally discourage the IC from proactively approaching the public. Since the WDDS concept and infrastructure are unclassified by their nature, the IC can describe and explain the initiative without restraint or fear of inadvertently disclosing non-public information. Additionally, WDDSs’ security benefits and limited intrusiveness offer a natural point of convergence and mutual interest to bridge the divide that separates the IC and its skeptics on other issues. Though advocates may be inclined to tie WDDSs to considerations surrounding more sensitive intelligence activities, an IC outreach team could lay the groundwork for more wide-ranging conversations through advance preparation and selective declassification of appropriate information.
This backdrop illuminates the contours of an effective outreach strategy to support WDDSs. First, the IC must establish a forum where public groups can engage an IC delegation in an atmosphere that nurtures honesty and trust. The IC’s outreach team should include representatives from a broad cross-section of the community who have extensive experience, relevant subject matter expertise, and substantial influence at their home agency. The membership of this team should remain stable over time to encourage cross-constituency relationships and partnerships. Finally, the outreach team should have a mandate to vet through IC leadership serious proposals emerging from this forum to strengthen privacy and civil liberties protections in IC programs.
Too often we in the IC bemoan the difficulty of executing our national security mission in a democracy. We cite the litany of advantages enjoyed by our adversaries operating in political structures where power is centralized, civil liberties are curtailed, communication channels are monitored, and the media and private industry act as organs of the government. This tilted playing field excites our fears, and foments doubt that democratic societies can remain secure.
The truth, however, is that America’s intelligence agencies have never in their history attempted to tap the most powerful resource unique to a democracy—its supporters. Swearing by secrecy as an article of faith, the IC blinds itself to the prospect of exponentially multiplying its intelligence capabilities by offering millions of people the choice to protect their democracy and way of life against catastrophic threats. The technology underlying WDDSs enables Americans to make this choice without betraying or sacrificing the rights and freedoms that distinguish us from our enemies. WDDSs only report the levels of nuclear, chemical, or biological agents in a specific location at a particular time. They are agnostic to the building blocks of a person’s private life—biographic information, biometric data, electronic accounts, communications content and metadata, social media activity, financial data, pattern of life, or any other identifying information.
Recent events offer a sobering reminder that traditional intelligence tools may be effective at anticipating attack plots, but they are not perfect. In July 2017, two men directed by ISIS attempted to create an improved chemical device to disperse “highly toxic hydrogen sulfide” in Sydney Airport. Two months later, ISIS-inspired attackers detonated a “bucket bomb” at a London subway station, injuring twenty-nine people. While the public demands an infallible capability to disrupt WMD attacks, this aspiration is unrealistic without a safety net that can secure through technical means the WMDs in our homeland that traditional intelligence tools fail to identify. Widely distributed detection systems may be the missing piece to a puzzle that has long vexed the government—but only if the IC can confront the modern WMD threat by learning to partner with the people it protects.
[*] This article was a winner of the Galileo Award in 2017, an annual competition sponsored by the Office of the Director of National Intelligence.
[†] Jonathan Fischbach is an attorney for the United States government. The positions expressed in this article do not necessarily reflect the views of any agency for which he works, or the views of the United States.
 Telephone interview with Dr. Ephraim Fischbach, Professor of Physics, Purdue University (Aug. 5, 2017).
 For an example of a system that would qualify, see Ephraim Fischbach & Jere Jenkins, Radiation Detection: There’s an App for That, 68 Bull. of the Atomic Scientists, 63, 63–64 (2012).
 U.S. Patent No. 7,994,926 (issued Aug. 9, 2011).
 Liz Harley, Just a SmidgION: Oxford Nanopore Announce iPhone-Powered Sequencing, Front Line Genomics (May 27, 2016), http://www.frontlinegenomics.com/news/5452/just-a-smidgion-oxford-nanopore-announce-iphone-powered-sequencing.
 Dalton T. Snyder, et al., 88 Miniature and Fieldable Mass Spectrometers: Recent Advances, Analytical Chemistry, 2, 2–3 (2016).
 See Flir Systems, Inc., Flir Griffin G510 2 (2018) (describing a portable mass spectrometer that can run on 100–240 volts alternating current); Melissa Ng, Power of a Car Battery, The Physics Factbook (2001), https://hypertextbook.com/facts/2001/MelissaNg.shtml (describing car batteries as producing 12 volts direct current); Power a Laptop or TV with a Car Power Adapter, Family Handyman, (last visited Aug. 30, 2018), https://www.familyhandyman.com/electrical/power-a-laptop-or-tv-with-a-car-power-inverter/view-all/ (describing widely available $30-$50 car mounted power inverters “that take 12-volt direct current (DC) and change it to 120-vold alternating current (AC)”); see also Jeremy Laukkonen, The Right Car Power Adapter Can Juice Up Your Electronics On the Road, Lifewire (Mar. 10, 2018), https://www.lifewire.com/juice-up-your-electronics-on-the-road-534756 (describing the use of power adapters to power household electronics from a car battery); Jeremy Laukkonen, Understanding Car Power Inverters, Lifewire (Mar. 22, 2018), https://www.lifewire.com/what-is-a-car-power-inverter-534721 (same). Cf. Snyder, supra note 5, at 2 (“In order to be portable, the electronics [of a portable mass spectrometer] should be rugged, inexpensive, and designed to minimize power consumption, enabling operation from battery power.”).
 See generally K. Lee Lerner, Weapons of Mass Destruction, Detection, Encyclopedia.com (2004), https://www.encyclopedia.com/politics/encyclopedias-almanacs-transcripts-and-maps/weapons-mass-destruction-detection (discussing the process and challenges of detecting WMDs).
 See Ershad Sharifahmadian, Yoonsuk Choi & Shahram Latifi, Remote Detection of Weapons of Mass Destruction using Wideband Radar, 121 Int’l J. of Computer Applications 20, 20 (2015) (discussing the power and promise of methods to physically detect the presence of WMDs).
 See Fischbach, supra note 2, at 65 (“One of the important reminders of the Fukushima accident is that the fallout drifts are carried by winds that are essentially a turbulent fluid. The random settling of fallout from this turbulence creates many hot spots, which a mobile phone-based system could help pinpoint.”).
 See, e.g., United States v. Knotts, 460 U.S. 276, 281 (1983) (holding that the Fourth Amendment does not prohibit the government from tracking a defendant’s movement along public streets).
 See Richard M. Thompson II, Cong. Research Serv., R42511, United States v. Jones: GPS Monitoring, Property, and Privacy 7–11 (2012).
 Significantly, the government’s passive receipt of WDDS data voluntarily provided by private citizens would not be considered a “search” for Fourth Amendment purposes. See Apodaca v. New Mexico Adult Probation And Parole, 998 F.Supp.2d 1160, 1174 (D.N.M. 2014) (“A Fourth Amendment search occurs either where the government, to obtain information, trespasses on a person’s property or where the government violates a person’s subjective expectation of privacy that society recognizes as reasonable to collect information.”) (citing United States v. Jones, 565 U.S. 400, 409 (2012)). As described supra, a WDDS would only convey information transmitted directly to the government by individuals voluntarily opting into the WDDS. Networked portable detectors do not report environmental data subject to a reasonable expectation of privacy; nor can this arrangement colorably be characterized as a trespass by the government. Cf. Carpenter v. United States, 138 S. Ct. 2206, 2220 (2018) (holding that the government’s review of defendant’s cell site location information was a Fourth Amendment search that required a warrant, even where this data was held by third party cell providers. The Court reasoned that “in no meaningful sense does the user voluntarily assume the risk of turning over a comprehensive dossier of his physical movements.”) (quotations and alterations omitted).
 See S. Rahman, D. Walker & P. Sultan, Medical identification or alert jewellery: an opportunity to save lives or an unreliable hindrance? 72 Anaesthesia 1139, 1142 (2017) (noting that the global population served by UK medical alert bracelet manufacturer MedicAlert numbers in the “millions” worldwide); Susan Gilbert, Lifesaving Medical History Coming in a Flash, N.Y. Times (Aug. 21, 1996) (noting that medical alert bracelets were worn by five million people worldwide in 1996), https://www.nytimes.com/1996/08/21/us/lifesaving-medical-history-coming-in-a-flash.html.
 Riley v. California, 134 S.Ct. 2473, 2489 (2014).
 See Thomas Young, 40 Years Ago, Church Committee Investigated Americans Spying on Americans, Brookings (May 6, 2015), https://www.brookings.edu/blog/brookings-now/2015/05/06/40-years-ago-church-committee-investigated-americans-spying-on-americans/.
 See Chris Inglis & Jeff Kosseff, Hoover Institution, In Defense of FAA Section 702: An Examination of Its Justification, Operational Employment, and Legal Underpinnings 5–7 (2016), https://www.hoover.org/sites/default/files/research/docs/ingliskosseff_defenseof702_final_v3_digital.pdf; Radio Address by George W. Bush, President of the United States (July 28, 2007), https://georgewbush-whitehouse.archives.gov/news/releases/2007/07/print/20070728.html (“In his testimony to Congress in May, Mike McConnell, the Director of National Intelligence, put it this way: We are ‘significantly burdened in capturing overseas communications of foreign terrorists planning to conduct attacks inside the United States.’ To fix this problem, my administration has proposed a bill that would modernize the FISA statute.”); FISA for the 21st Century: Hearing Before the S. Comm. on the Judiciary, 109th Cong. 2 (2006) (statement of Gen. Michael V. Hayden, Director, Central Intelligence Agency) (requesting and commenting on modernization of FISA); see also H. R. Rep. 95-1283, pt. 1, at 27-28 (1978) (“The committee has explored the feasibility of broadening this legislation to apply overseas, but has concluded that certain problems and unique characteristics involved in overseas surveillance preclude the simple extension of this bill to overseas surveillance.”); Foreign Intelligence Surveillance Act of 1978: Hearings Before the Subcomm. On Intelligence and the Rts. of Ams. Of the S. Select Comm. on Intelligence, 95th Cong. 47 (1978) (statement of Adm. Stansfield Turner, Director, Central Intelligence Agency) (“[A]s to the idea of broadening the provisions of the bill so as to make them applicable to electronic surveillance activities conducted abroad, I believe that such a step would be inappropriate and unwise.”)
 See Abigail Geiger, How Americans have viewed government surveillance and privacy since Snowden Leaks, Pew Res. Ctr. (June 4, 2018), http://www.pewresearch.org/fact-tank/2018/06/04/how-americans-have-viewed-government-surveillance-and-privacy-since-snowden-leaks/ (“Americans became somewhat more disapproving of the government surveillance program itself in the ensuing months, even after then-President Barack Obama outlined changes to the NSA data collection.”).
 See Jake Laperruque, How Congress Should Evaluate Section 702’s Security Value When Debating Its Reauthorization, Lawfare (June 16, 2017), https://www.lawfareblog.com/how-congress-should-evaluate-section-702s-security-value-when-debating-its-reauthorization (“Even Congress’ most vociferous privacy watchdogs . . . acknowledge the value of Section 702 and are not demanding its expiration.”); see also Laura K. Donohue, Section 702 and the Collection of Int’l Telephone and Internet Content, 38 Harv. J. L. & Pub. Pol’y 117, 150–152 (2015); Elizabeth Goitein & Faiza Patel, Brennan Center for Justice, What Went Wrong with the FISA Court 28 (2015).
 See Timothy H. Edgar, Hoover Institution, Go Big, Go Global: Subject the NSA’s Overseas Programs to Judicial Review 8 (2016) (“Today, the only way to fully protect Americans’ privacy is to subject the NSA’s global programs of surveillance to the scrutiny of all three branches of government, which means subjecting them to FISA. One way to do this is suggested by the much maligned section 702 of FISA. A reformed section 702 of FISA could be the model for a new provision in title VII of FISA requiring authorization of the NSA’s global surveillance programs by the Foreign Intelligence Surveillance Court.”), https://www.hoover.org/sites/default/files/research/docs/edgar_webreadypdf.pdf.
 See Ewen MacAskill, The NSA’s bulk metadata collection authority just expired. What now?, The Guardian (Nov. 28, 2015), https://www.theguardian.com/us-news/2015/nov/28/nsa-bulk-metadata-collection-expires-usa-freedom-act.
 See Laperruque, supra note 15 “As I’ve written previously, the government’s ability to freely use Section 702 data to investigate any federal crime is a serious problem.”).
 See Mana Azarmi, Urgent Fix Needed: USA Liberty Act Needs to Better Focus Surveillance Under FISA 702, Ctr. For Democracy and Tech. (Oct. 20, 2017), https://cdt.org/blog/urgent-fix-needed-usa-liberty-act-needs-to-better-focus-surveillance-under-fisa-702/ (“[T]he problem remains that the definition of foreign intelligence information includes catchalls that allow the government to capture content merely related to ‘the conduct of the foreign affairs of the United States’ or to the ‘national defense or the security of the United States.’ This sweeps in a lot of innocent conduct.”).
 See The White House, Presidential Policy Directive 28: Signals Intelligence Activities (Jan. 17, 2014) [hereinafter PPD-28], https://obamawhitehouse.archives.gov/the-press-office/2014/01/17/presidential-policy-directive-signals-intelligence-activities (“[O]ur signals intelligence activities must take into account that all persons should be treated with dignity and respect, regardless of their nationality or wherever they might reside, and that all persons have legitimate privacy interests in the handling of their personal information.”).
 See Colin Moynihan, A New York City Settlement on Surveillance of Muslims, The New Yorker (Jan. 7, 2016), https://www.newyorker.com/news/news-desk/a-new-york-city-settlement-on-surveillance-of-muslims (“One lawsuit, filed in federal district court in Brooklyn by the American Civil Liberties Union and others, maintained that more than a decade of ‘suspicionless surveillance’ of Muslims had violated the Constitution and ‘profoundly harmed’ thousands of people whose names were placed in secret police files.”); see also Elizabeth Stoycheff, Under Surveillance: Examining Facebook’s Spiral of Silence Effects in the Wake of NSA Internet Monitoring, 93 Journalism & Mass Comm. Q. 296, 307 (“For the . . . majority . . . of participants, being primed of government surveillance significantly reduced the likelihood of speaking out in hostile opinion climates. . . . This is the first study to provide empirical evidence that the government’s online surveillance programs may threaten the disclosure of minority views and contribute to the reinforcement of majority opinion.”)
 Kolender v. Lawson, 461 U.S. 352, 357 (1983).
 See PPD-28, supra note 18.
 See id., at Sec. 1(b).
 See, e.g., U.S. Off. of The Dir. of Nat’l Intelligence, Intelligence Cmty. Directive 107, 2 (2018), https://fas.org/irp/dni/icd/icd-107.pdf; About CIA: Privacy and Civil Liberties at CIA, U.S. Central Intelligence Agency (Mar. 26, 2018, 7:05 p.m.), https://www.cia.gov/about-cia/privacy-and-civil-liberties.
 See Jacqueline Williams, Australia Details ‘Sophisticated’ Plot by ISIS to Take Down Plane, N.Y. Times (Aug. 4, 2017), https://www.nytimes.com/2017/08/04/world/australia/sydney-airport-terror-plot-isis.html.
 Sewell Chan, Patrick Kingsley & Ceylan Yeginsu, ‘Bucket Bomb’ Strikes London’s Vulnerable Underground, N.Y. Times (Sept. 15, 2017), https://www.nytimes.com/2017/09/15/world/europe/uk-london-underground-tube-explosion.html.