Police in Florida aren’t allowed to use a cellphone to track someone’s movements according to a sweeping new ruling from the Florida Supreme Court.

The court by a 5-2 vote ruled Thursday that authorities in Broward County had no right to stop and arrest Shawn Tracey for possession of more than 400 grams of cocaine.

The police had a warrant to tap his cell phone calls, but that warrant didn’t include authorization to use his cell phone to track him.

This is entirely appropriate. If the police want to invade a citizen’s privacy, they need either to convince a court that they have probable cause for that, or they need to actually and overtly invade: in the present context, to assign a cop to follow him around.

One of the two dissenting justices, Charles Canady, though, misunderstands the concept of privacy. He cited the US 5^th Circuit as follows:

Because a cell phone user makes a choice to get a phone, to select a particular service provider, and to make a call, and because he knows that the call conveys cell site information,…he voluntarily conveys his cell site data each time he makes a call.

Canady added under his own thinking,

Given the known realities of how cell phones operate—realities understood and accepted by all but the most unaware—…cell phone users have neither a subjective expectation of privacy nor an objectively reasonable expectation of privacy regarding the cell site information generated by their cell phones.

Of course the cell phone user does, on both counts. Notice, as Canady apparently does not, that the voluntary conveyance of the information is to a private enterprise, not to a government entity. We citizens can, and we do, have a very strong expectation of privacy regarding any information we surrender to a private entity as a necessary requirement for that entity to provide the service for which we’re paying it.

Notice further, that the caller expects that private enterprise to safeguard our private information, whether it’s surrendered so that the enterprise becomes able to provide the contracted service or whether it’s surrendered more voluntarily as a non-necessary adjunct to that service. This is made clear by the public’s—us people’s—hue and cry over such trackings, by any entity, commercial or otherwise.

If a government entity wants to invade a man’s privacy, it must convince a court of sufficient probable cause as to get a warrant authorizing the invasion. As the police understood in the present case, when they got the warrant to tap Tracey’s cell phone calls—and chose not to get a warrant to collect his location data.

The Court’s ruling, including Canady’s dissent, can be seen here.