One of the more interesting Fourth Amendment issues created by our ubiquitous use of cell phones involves law enforcement obtaining historical records of our cell phone’s location in order to determine where we were at any given time in the past.  The Eleventh Circuit recently ruled in United States v. Davis in that the government must obtain a warrant before it can access this information; the case is now on appeal to the entire circuit en banc.

This issue has already been considered by the Third Circuit and the Fifth Circuit, both of which refused to apply the Fourth Amendment to the acquisition of historical cell phone location data.  But in Davis, the government received over 11,000 records of the defendant’s location–one for every eight seconds during the sixty-seven days covered by the records.  In order to acquire these records, the government did not seek a warrant, because the prosecutor argued that under the third party doctrine of Smith v. Maryland, a warrant was unnecessary. (The government did obtain a “D-order” under 18 U.S.C. § 2703(d) of the Stored Communications Act, which only requires that the government demonstrate “specific and articulable facts” that the information is “relevant and material” to an ongoing criminal investigation).

The judgment of the Davis case is consistent with Justice Alito’s concurring opinion in United States v. Jones.  The Jones concurrence held that although following a car over public highways for one trip was not a Fourth Amendment “search,” tracking the movements of a person’s car over public highways for one month did constitute a search.   In Davis, the government tracked the defendant’s movements for sixty-seven days; thus, under the mosaic theory of the Fourth Amendment, tracking the defendant for such an extended period of time violated his reasonable expectation of privacy.   Thus, there is a good chance that on these facts, the Eleventh Circuit might uphold the judgment of the three-judge panel.

But the underlying holding of the Davis case did not rely on the mosaic theory.  The court went further and held that any use of cell phone location data constituted a search:

“Davis has not voluntarily disclosed his cell site location information to the provider in such a fashion as to lose his reasonable expectation of privacy.

In short, we hold that cell site location information is within the subscriber’s reasonable expectation of privacy. The obtaining of that data without a warrant is a Fourth Amendment violation. Nonetheless, for reasons set forth in the next section of this opinion, we do not conclude that the district court committed a reversible error.”

The ACLU has duly filed an amicus brief for the en banc appeal in Davis, urging the panel to let the original decision stand.  A lawyer for the ACLU explained their position in a recent article in the Wall Street Journal:

“[Cell phone location information] gives the police a power that they have never had before in the history of law enforcement, which is a time machine into where somebody was going and what somebody was doing in the past,” said Nathan Freed Wessler, an American Civil Liberties Union lawyer who has also filed a brief in the case. “It’s an incredibly powerful investigative tool. And with an appropriate warrant police can get that, but what is absolutely essential is they can’t just sort of walk their way into that time machine without demonstrating probable cause.”

Thus, according to the Eleventh Circuit’s opinion, the government should never be able to use the positional information from our cell phones to learn our past location, even if the government is only seeking records from one specific point in time.  The ACLU argues that this is analogous to using a “time machine” to spy on our past movements, and argues that police have never before had this power.  But this is surely an exaggeration.   This type of “back-dated” surveillance is quite common.  Surveillance cameras in public places have been around for decades.  And the government has routinely used historical data to track the past movements of suspects–they could tell when a certain car entered a parking garage or crossed a toll bridge; they could check the person’s home phone logs and determine whether the person was present at home at a certain time;  they could tell when a person punched in at work; and so on.

As is usually the case, the difference between historical cell phone location data and other, more familiar types of historical surveillance is a difference in degree, not kind.  Cell phone location data makes law enforcement more efficient–if the police want to know whether a suspect was at a certain location at a certain time, they are much more likely to be able to determine that fact now than they were in the past with more traditional techniques.  As the government notes in its brief, this type of information can absolve the innocent as well as inculpate the guilty; the innocent suspects would then be spared being the subject other, far more intrusive surveillance and investigative techniques.

If we apply the Katz test to this question, it seems unlikely that an average person would believe that they have a reasonable expectation of privacy in their physical location.  The vast majority of people make no secret of their physical location at any given time; the very idea that their location should be kept secret would strike them as strange.  It is only when the government is trying to obtain massive amounts of information covering an extended period of time that the mosaic theory kicks in that the government begins to learn truly private information about the person, thus transforming this surveillance into a Fourth Amendment search.

Granted, there are certain times when individuals–both the innocent and the guilty–would like their location to be secret.  But if that is the case, we would expect a reasonable person to take precautions so that others would not know where he or she was.  In the past, that would perhaps mean wearing a disguise, or sneaking away at night, or avoiding populated areas.  In the modern era, it now also means turning a cell phone off, or leaving the cell phone at home, or using a cell phone that cannot be traced back to its user.  This requires extra effort on the part of the individual who wishes to remain hidden,  but–again–this is not a new phenomenon.  For example, assume a person wishes to make a secret trip to a motel.  The most convenient method of doing so would be for her to drive her own car and park it outside the motel.  But this runs the risk of somebody seeing  the license plate on the car, either while it is being driven or while it is parked outside.  Thus, to ensure secrecy, the person must either walk, or use a different car, or park some distance from the motel.  Does imposing these restrictions mean that the person’s reasonable expectations of privacy are being violated?  Should we therefore preclude police from the conducting  warrantless checks of the license plates of cars that are in public view?

Certain technological advances–such as cars and cell phones–have become ubiquitous because they provide an enormous increase in convenience.  As it turns out, these advances also provide the police with more efficient tools to conduct criminal investigations.  As long as these tools are not revealing previously secret, hidden, private information (and a person’s physical location does not seem to fit into that category), it makes sense to allow the police to use these tools to save resources, track down the guilty, and exonerate the innocent.