But the tangled factual record, uncertainty about where technology is heading and occasionally muddled advocacy pointed toward a limited ruling that might provide little guidance to government employers and perhaps none to private ones.
“I just don’t know how you tell what is reasonable,” Chief Justice John G. Roberts Jr. said. “I suspect it might change with how old people are and how comfortable they are with the technology.”
The Supreme Court has said the Fourth Amendment, which forbids unreasonable government searches, figures in the analysis when public employers search their employees’ offices and files.
The chief justice appeared sympathetic to the police officer in the case, Sgt. Jeff Quon of the Ontario Police Department’s SWAT team, who had received mixed guidance from his superiors about the status of messages sent on his pager. The messages included communications to and from his wife and his mistress.
The department’s written policy allowed “light personal communications” but cautioned employees that they “should have no expectation of privacy.” Under an informal policy adopted by a police lieutenant, however, those who paid for messages over a monthly maximum would not have their records inspected.
Chief Justice Roberts said the combination of the two policies might be enough to give Sergeant Quon a reasonable expectation of privacy under the Fourth Amendment. “I think if I pay for it,” the chief justice said, “it’s mine and not the employer’s.”
Neal K. Katyal, a deputy solicitor general, disagreed, saying that a low-level employee had no power to change a general policy. “The computer help desk cannot supplant the chief’s desk,” Mr. Katyal said.
Justice Stephen G. Breyer said that a certain amount of personal texting was to be expected. “You want to let them have a few,” Justice Breyer said. “You need pizza when you are on duty.”
Chief Justice Roberts warned against devising a legal rule that “would require people basically to have two of these things with them, two of whatever they are — the text messager or the BlackBerrys or whatever.”
Justices John Paul Stevens and Anthony M. Kennedy indicated that SWAT team members might be treated differently from other government employees because their records are often subject to disclosure in lawsuits or under California’s open-records law.
The harder question, several justices suggested, was that of the privacy of the people with whom Sergeant Quon communicated.
There was some confusion, too, about the technology at issue in the case, City of Ontario v. Quon, No. 08-1332.
“What happens, just out of curiosity,” Chief Justice Roberts asked, “if he is on the pager and sending a message and they are trying to reach him for, you know, a SWAT team crisis? Does the one kind of trump the other, or do they get a busy signal?”
Dieter Dammeier, a lawyer for Sergeant Quon, said he was not sure.
Justice Kennedy suggested that the caller might get a recorded message.
“He’s talking to the girlfriend,” Justice Kennedy said, and the caller “gets a voice message that says: ‘Your call is very important to us. We will get back to you.’ ”
Separately, in an unsigned order issued Monday, the court declined to hear an appeal from Charles D. Hood, a death row inmate in Texas who had sought a new trial given evidence that the judge in his case had had an affair with the prosecutor. As is customary, the court gave no reasons for its decision.