Librarians, the news media, defense lawyers and civil liberties groups on the right and left are trying to convince the justices that they should take a broad view of the privacy issues raised when police have unimpeded access to increasingly powerful devices that may contain a wealth of personal data: emails and phone numbers, photographs, information about purchases and political affiliations, books and a gateway to even more material online. “Cellphones and other portable electronic devices are, in effect, our new homes,” the American Civil Liberties Union said in a court filing that urged the court to apply the same tough standards to cellphone searches that judges have historically applied to police intrusions into a home. Under the Constitution’s Fourth Amendment, police generally need a warrant before they can conduct a search. The warrant itself must be based on “probable cause,” evidence that a crime has been committed. But in the early 1970s, the Supreme Court carved out exceptions for officers dealing with people they have arrested. The court was trying to set clear rules that allowed police to look for concealed weapons and prevent the destruction of evidence. Briefcases, wallets, purses and crumpled cigarette packs all are fair game if they are being carried by a suspect or within the person’s immediate control.