You can't know that a priori, though. The cops should not get to say "I want to track this cell phone, it's being used for a crime" without filing a warrant. Th

You can't know that a priori, though. The cops should not get to say "I want to track this cell phone, it's being used for a crime" without filing a warrant. That is pretty much exactly what warrants are for in other contexts, cell phones should not be treated differently.