I recently came across an interesting Fourth Amendment case in which a district court judge ruled that a defendant has no privacy rights in the list of phone numbers stored inside his cell phone: United States v. Fierros-Alavarez, 547 F. Supp.2d 1206 (D. Kan. 2008). This conclusion is wrong, I think, and why it's wrong raises an interesting aspect of Fourth Amendment law.

  The facts of the case are simple. The defendant was arrested and taken into custody, and a cell phone was taken from him at the time. The next day, the officers began to suspect that the cell phone stored records of criminal activity. Specifically, the officers believed that the defendant was a participant in a narcotics conspiracy, and that there would be records of calls to other members of the conspiracy inside the phone. Acting without a warrant, an officer searched three parts of the phone:

He looked at its "phone book" directory that stores names and telephone numbers, and he recorded the five names found there. He checked the recent calls directory that retains the telephone numbers of missed, received or dialed calls, and he wrote down the telephone numbers for the twenty recent calls. He checked the picture and video file but found nothing.

  The evidence was later used against the defendant to prove the case against him, and he moved to suppress the evidence on the ground that the officer violated his Fourth Amendment rights in looking through the phone. To resolve that issue, the court first addressed the threshold issue of whether the officer's retrieving the phone numbers violated the defendant's reasonable expectation of privacy.

  That threshold question forced the court to choose between two different lines of cases. On one hand, there are the cases concluding that a defendant normally has a reasonable expectation of privacy in the contents of data stored in his phones, pagers, and computers. On the other hand, there is Smith v. Maryland, 442 U.S. 735 (1979), in which the Supreme Court held that it does not violate a defendant's reasonable expectation of privacy to install a "pen register," a device for recording the numbers dialed from a particular phone line, at the office of the phone company.

  The basic question for the district court in Fierros-Alavarez was whether the Fourth Amendment rule for retrieving numbers dialed for a phone should follow the precedent for the device or the precedent for the data. The court concluded that the case was governed by Smith, and that therefore retrieving the data was not a search:

The government argues the holding in Smith and the later applications of Smith logically extend to the issue presented by the facts of this case so as to preclude an expectation of privacy in the recent call directory as well as the phonebook directory. The defendant's only rejoinder is that a phone book directory may disclose more information than that revealed in a pen register. The defendant, however, has not shown that the phone book directory in his cellular telephone discloses more than the "addressing information"-the telephone number and the subscriber's name-on the same numbers appearing in the recent calls directory. On the record as it stands, the court must conclude that the defendant has not carried his burden of proving a reasonable expectation of privacy in the addressing information retrieved from the recent calls directory and in the names and numbers taken from the phonebook directory. Thus, the court denies the defendant's motion for lack of standing.

  Wrong conclusion, I think. The general rule for Fourth Amendment searches is that privacy rights are determined ex ante by the place in which the search occurs, not ex post by whether the evidence turns out to be private. If a person has a storage device like a phone, computer, or package, Fourth Amendment rights are determined by whether the person has rights in the storage device, not whether the particular information discovered was sufficiently "private" to deserve Fourth Amendment protection.

  The leading case here is probably Arizona v. Hicks, 480 U.S. 321 (1987). In Hicks, an officer entered an apartment under exigent circumstances to try to find and stop a person who was firing gunshots from inside the apartment. Once inside, the officer saw very expensive stereo equipment in what was otherwise a squalid apartment. Suspecting that the equipment was stolen, the officer picked up the equipment to see the serial numbers so he could run the numbers for hits with known stolen property. In an opinion by Justice Scalia, the Court held that moving the equipment to reveal the serial numbers was a search:

It matters not that the search uncovered nothing of any great personal value to respondent - serial numbers rather than (what might conceivably have been hidden behind or under the equipment) letters or photographs. A search is a search, even if it happens to disclose nothing but the bottom of a turntable.

  That rule makes a lot of sense, I think. The police shouldn't be allowed to go through your private stuff so long as they only look for and take information that is in some sense "non-private." If you write a diary entry and describe going for a walk in the park, the police shouldn't be allowed to break into your home, rifle through your stuff, read your diary, and then take the entry about walking in the park all on the theory that the fact that your walk in the park was "public."

  The same goes for the numbers dialed stored in the cell phone in Fierros-Alavarez. Sure, if the police had installed a pen register in the phone and collected the information at the phone company, then collecting the number dialed wouldn't have triggered the Fourth Amendment. But the police didn't do that. And the police can't go hunting through private things like cell phones on the theory that they're only looking for information that they could have collected constitutionally if they had only thought of it at the time. Numbers dialed that are stored in a cell phone are normally protected by the Fourth Amendment as much as anything else stored in a cell phone, and it was wrong to say that Smith required a different result.

  There's a broader point at issue here: Fourth Amendment rights are contextual. Data, whether in the form of numbers (like telephone numbers here) or text (in the case of a diary), does not have a preordained level of Fourth Amendment protection in the abstract. If you store your diary at home under your bed, you have Fourth Amendment rights in your diary because you have stored in it your home. If you go into the park and leave your diary out in the open, you lose Fourth Amendment rights in what you have left open because you have left it open. The Fourth Amendment rights derive from the steps that the government must go through to retrieve the information in context, not the essential nature of the data itself.

  Finally, I should point out that there are some interesting possible exceptions to this general rule in cases involving digital contraband. This case doesn't involve contraband, though, so I'll just flag that possibility for now; see Richard Salgado's essay for more.