Skip to main content
Find a Lawyer

Every Move You Make, Part Three: Why Law Enforcement Should Have to Get a Warrant Before Tracking Us Via our Cell Phones


Thursday, Nov. 10, 2005

Should law enforcement personnel have to obtain warrants, upon a showing of probable cause, before they track our movements - potentially, in real time -- by obtaining "cell site data" from our cell phone companies?

Two federal courts - in Texas and in New York -- recently said yes.

And as I will explain, they were right to do so. (In a previous column, I argued that it was okay for state government to monitor cell phones in traffic, but not for criminal law enforcement purposes - for traffic control).

We have a reasonable expectation of privacy with respect to our movements, as we go about our daily business. Though sometimes we may be seen by passersby and by security cameras, at other times we will not be; and sometimes, we will be in the privacy of our own homes or offices when we carry our cell phones. Our expectation of privacy should be honored, as the Texas and New York courts held.

But other courts in other jurisdictions have held otherwise. For that reason, Congress should now step in and ensure, by statute, that the warrant requirement applies under these circumstances.

The balance of privacy and security is a delicate one - and the warrant requirement is an appropriate check on law enforcement's ability to track, via cell phone data, every move we make.

The Surveillance Orders the Government Sought

These cases began when Department of Justice ("DOJ") officials asked judges in Texas and Long Island, respectively, to approve court orders directed at cell phone providers, requiring them to turn over subscriber records and cell phone location data for certain customers.

At the same time, the DOJ asked that the courts issue an order allowing the installation of "pen registers" - which record the numbers of outgoing calls -- and "trap and trace devices," which capture the phone numbers of incoming calls.

In Texas, the government asked for "the location of cell sites at call origination and termination and if possible during the progress of a call." Also sought was "information regarding the strength, angle, and timing of the caller - signal measured at two or more cell sites, as well as other system information such as listing of all cell towers in the market area. . . "

This information, collectively, is referred to as "cell site" data. It can help track a person because, as the court noted, a cell phone acts as "a radio transmitter that automatically announces its presence to a cell tower via a radio signal over a control channel which does not itself carry the human voice. By a process of triangulation from various cell towers, law enforcement is able to track the movements of the target phone and hence locate a suspect using the phone." Notably, this process can occur even when a phone is idle; you need not be talking, to be tracked.

Even if the data sought is not quite precise yet, it very soon will be. By the end of 2005, cell phone carriers using handset-asked location technology will be required to locate cell phones within 150 meters for 95% of calls as part of an E-911 policy.

In New York, the DOJ sought an order to record the location of the cell towers that handled a call using information in a cell phone's "control channel." This data would give a rougher approximation of a user's locations and movement, than would the triangulation data DOJ sought in Texas.

The Key Question: Which Statutory Surveillance Category Did DOJ's Requests Fall Into?

In neither case did DOJ assert that it had probable cause to believe a crime had occurred, or was in progress. Instead, it simply asserted that the information collected would be "relevant" to an investigation. For this reason, it was crucial which federal statutory provision - and thus which standard - would be applied.

The Electronic Communications Privacy Act of 1986 (ECPA) sets forth standards for various types of electronic surveillance: The more intrusive the surveillance, the higher the burden on law enforcement to show why it is needed. (The background of this statute - and the source of the "probable cause" requirement, in some case, is the Constitution's Fourth Amendment.)

The "relevant and material to an ongoing criminal investigation" standard is a low one. It is applicable to surveillance using a pen register and a trap/trace device. But, significantly, the Communications Law Enforcement Assistance Act expressly prohibits the use of pen/trap orders for tracking subjects' location.

The reasoning behind applying a low standard to pen/trap orders is that we do not have a very high expectation of privacy in the telephone numbers we dial.

(In contrast, actual wiretapping by the government - that is, the government's overhearing the contents of our conversations -- requires a warrant. And relevance is not enough: The warrant must be granted upon a showing of probable cause that a crime has been committed, or is occurring. Since the crime can be the crime of conspiracy, this standard still gives the government quite a bit of latitude.)

Another area in which the government has to meet a lower threshold than probable cause is that of "subscriber records," concerning electronic communications service or remote computing service. The government has to provide "specific and articulable facts . . . showing reasonable grounds to believe that . . .the records are . . .relevant to and material to an ongoing criminal investigation." The Stored Records Act (SRA) permits access to "stored" subscriber records. Examples might be one's cell phone billing history, or records of one's old calls.

Before the Texas and New York judges, the DOJ claimed that future, prospective cell site data counted as a stored record- for as soon as the data was gathered, DOJ said, it was stored and became a record.

But the judges rightly saw through this argument - holding that the stored records category was meant to apply to records already existing or being made before permission to surveil was granted. If not, then the government could conduct any surveillance it wanted as long as it made a record of what it was doing at the same time!

Both judges said that the cell site data requests constituted not requests for stored records but, in effect, requests to use a mobile "tracking device" -- requests which, under the law, require a warrant.

As Judge Orenstein, the New York judge, wrote, "When the government seeks to turn a mobile telephone into a means for contemporaneously tracking the movements of its user, the delicately balanced compromise that Congress has forged between effective law enforcement and individual privacy requires a showing of probable cause."

Finally, the DOJ also argued that the expanded definition of pen/trap devices under the USA Patriot Act, when read in conjunction with other statues such as the ECPA and the SRA, allowed for collection of cell site data. (The Patriot Act amends the definition of pen/trap devices to include "dialing, routing, addressing and signaling information.")

But both judges pointed out that this expansion was plainly meant to allow surveillance of electronic communications such as email - not to widen the type of surveillance that could be conducted without probable cause

Congress Needs To Clarify the Warrant Requirement for Cell Phone Tracking

Both judges concluded that Congress needed to clarify the scope of existing electronic surveillance laws as they apply to cell site tracking. Currently, both the House and Senate are debating the details of the Patriot Act reauthorization. At present, it appears unlikely that any proposed bill will clarify the cell phone tracking issue, without specific proposals about this issue.

Cell site data is unquestionably a powerful and valuable tool for law enforcement. It can help the government catch fleeing suspects and fugitives. But equally, such data can drastically infringe an individual's privacy, allowing the government to track him almost as surely as if he had a GPS implant under the skin. For this kind of surveillance, probable cause should be required - and Congress should make that clear.

Anita Ramasastry is an Associate Professor of Law at the University of Washington School of Law in Seattle and a Director of the Shidler Center for Law, Commerce & Technology. Her other columns on privacy, surveillance, and other issues are included in the archive of her columns on this site.

Was this helpful?

Copied to clipboard