Data Suggests that Public Does Not Support Warrantless GPS Tracking


A UC Hastings law student has performed an excellent experiment to test the viability of the Katz two-prong test.  The Katz test issued to determine whether police actions of the constitute a “search” within the meaning of the Fourth Amendment. The Katz test asks (1) whether there was a subjective expectation of privacy and (2) if so, whether the expectation of privacy is one that society is willing to recognize as reasonable.

The full paper can be found here:  Herding Katz: GPS Tracking and Society’s Expectations of Privacy in the 21st Century by ZACHARY GRAY*

The study asked “everyday people whether they believed that GPS tracking violated their own personal sense of privacy expectations.”  321 randomly selected individuals were asked about the use of GPS tracking devices by answering questions about four potential scenarios in which the police used GPS devices to track an individual’s movements. The questions were asked in a way that allowed respondents who “believed that the officer’s actions were unjustified, yet also felt that the individual still did not have a reasonable expectation of privacy to answer accordingly; ensuring that people who disagreed with the officer’s actions but did not believe the suspect’s privacy was violated to say so without feeling compelled to agree with the premise that his privacy was violated to channel their disapproval of the officer’s actions.”

The results, according to the author,  suggest that “society overwhelmingly believes that GPS tracking is unjustifiable and violates an individual’s privacy rights.”  In particular, the study found that the use of GPS devices based on limited probable cause for an extended period of time was a as a violation of privacy rights.  Notably, the study found that the length of time for GPS monitoring was not important, as respondents seemed as critical of tracking that occurred for 48 hours as for four months.  The results did not change much when the facts were changed to provide greater probable cause to believe that criminal activity had occurred.  The author writes:

From circumstances in which the State has probable cause to believe an individual is engaged in criminal activity to those in which the belief is merely a hunch—and from tracking that lasts anywhere from four months to 48 hours—society consistently recognizes that GPS tracking is unjustified. The strong inverse correlation between the belief that it is justified and the belief that it violates expectations of privacy indicates a strong correlative and arguably causal relationship between these beliefs.

Interestingly, the study also asked respondents about a scenario  modeled after the facts in the original Katz decision – police monitoring of a call from a payphone.  Based on this study, most people agreed that privacy rights had been violated in Katz.  The author wrote,

it is clear that Katz was correct when it held that an individual’s expectation of privacy inside of a phone booth is an expectation that “society is prepared to recognize as reasonable.”152 Despite the anachronistic nature of a phone booth in contemporary society, respondents clearly believed that state action to monitor the conversation taking place inside that phone booth violated a clearly defined privacy norm and that it was unjustifiable for the authorities to do so.

The study found that men and women answered the questions about the same.  However, the data suggest that different ethnic groups “have marginally different privacy expectations and in some cases, significantly different perspectives on what degree of state intrusion they are willing to tolerate as justifiable.”

Empirical data is always better than conjecture — kudos to Mr. Gray on his work.


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