The Court decided that once someone is arrested, the police may not search the person's phone without a warrant.
The ruling stated that "the term 'cell phone' is often misleading in shorthand; many of these devices are in fact miniature computers that also happen to have the capacity to be used as a telephone. They could just as easily be called cameras, video players, rolodexes, calendars, tape recorders, libraries, diaries, albums, televisions, maps, or newspapers."
Before just about every single person in America carried a cell phone, the courts permitted police officers to search "from incident to arrest" in "that area into which he might reach." The meant that in order to prevent any sort of destruction or damage to evidence, law enforcement could search the data, contacts, messages, videos, photos, or other apps, on a person's cellphone if it was gathered into evidence once the person was arrested.
Now, in the course of an arrest, if police want to look into a suspect's phone, they will need a warrant. The decision is huge in terms of protecting citizens's rights to privacy, and is a ringing endorsement of digital privacy.
Here are a few reponses to the news:
This last response is why this decision is pivotal to American privacy rights in general. The hope is that because the wording in the Supreme Court ruling covers so much ground, NSA surveillance could be reeled in as well.