The Stingray & the 4th Amendment

There is a very interesting article today in the WSJ on the Stingray and the implications of its use against U.S. citizens.

The Stingray is basically a small suite of equipment and antennas that are used to create a vehicle borne mobile cell phone tower.  FBI agents or other law enforcement personnel can utilize the Stingray to track a cell phone that is powered on, whether the phone is in use (making a call or sending a text) or not.

Here's the short version of how without all the geek-speak.   First of all, you need to remember that your cell phone is a radio (actually as many as six different radios, but that gets too geeky to explain).   In order for the cell phone you have in your pocket, purse, or hanging on your belt to work properly, it needs to know which cell tower is closest to it.  Knowing that, the phone can communicate, via the built in radio, with the tower giving it the strongest signal.  As you walk or drive, the phone switches from the tower you were using that is now getting farther away, to the next closest tower as the signal from it gets stronger.  When the phone talks to the tower, it uses its unique (in the whole world) electronic identity to identify itself to the tower (actually, to the telephone network the tower connects your phone to).  The tower (and the telephone network behind it) knows how many phones it can reach, and 'talk' to, to allow you to make calls, send text messages, surf the web, etc.

This is where the Stingray comes in.  If a law enforcement agency can determine the electronic identifier your phone has assigned to it, they can go to a judge, apply for a search warrant, and then use the Stingray to find, and if needs be, track you.

They (law enforcement) load your phone's unique electronic identifier into the Stingray, then drive around in the vicinity of where they suspect you are, waiting for your phone to 'talk' to the Stingray.  Why would your phone talk to the Stingray instead of the cell tower nearby?  Because the Stingray broadcasts the same beacon a cell tower does, but because it's closer to your phone than the tower is, the signal appears stronger to the phone, and the phone is designed and programmed to lock on to the strongest signal.  After your phone is 'hooked' by the Stingray, then it's just a matter of old fashioned direction finding to track you and your phone.

(For those of you more technically inclined, yes I omitted a large amount of technical and procedural detail on purpose.)

I think the technology is very impressive and presents a number of advantages for law enforcement and other applications.  Having said that, it does create a 4th Amendment search and seizure issue for the courts, which will undoubtedly take time to resolve and yet again proves that the creation and interpretation of technology law lags behind the speed of technology.

It's illegal to wiretap someone's conversations without a court order.  Is it illegal to use what could be argued as the 'publicly available functions' of your phone to track you, particularly once you are outside your home, walking around in public?   Do you have a right to privacy if your phone is powered on, no matter where it (and you) are?

This technology, much like the similar controversy over law enforcement attaching GPS devices to suspect's vehicles to track their movements, will be a debate within the legal system worth watching.