There are almost too many exceptions to the warrant requirement to count; courts have acknowledged a plethora of situations in which officers need not seek judicial approval before conducting a search. You can read about many of them here.
In general, whatever a private citizen—rather than a police officer—uncovers through an
Do the Police Need a Warrant to Track You With Your Cellphone?
Cellphones, smartphones, smart devices, and even our vehicles track and store amazing amounts of data on our movements and whereabouts. Is this information protected by the Fourth Amendment? Well, legally speaking, it depends.