I listened to the NPR story when it ran. The FBI explained that they use these devices to <i>establish</i> probable cause, which they'd then use (ideally) to get a warrant for more invasive processes.<p>But as pointed out, if >90% of your cases already can meet that threshold according to a (theoretically) independent judiciary, then you don't really have a problem. Perhaps the other 10% reflected the abuses we want to prevent, or perhaps just sloppy police work.<p>Either way, the warrant requirement is a security control against abusive law enforcement. After all, by their own reasoning, if they've done nothing wrong, then they've nothing to hide (from a judge), right?<p>Interestingly, the story concluded by noting that the FBI would probably just depend more often on cell phone tracking records, which companies will often provide in response to a prosecutorial subpoena even without a judge's signature.