The 11th Circuit held that a defendant's cell phone tower data (i.e., general location of where the defendant was on a certain day and time) obtained by the police from a cell phone carrier is a search within the meaning the 4th Amendment. This puts them at odds with the 5th and 6th Circuits, opening the possibility of the Supreme Court granting cert sometime soon.
The use of generic cell phone tower data appears very similar to the pen register used in Smith v. Maryland (1979). If the police, as in Smith, can request the phone numbers someone dialed from their phone located inside their home, it is not much of a stretch to ask the same phone company for a person's whereabouts on a certain day and time without a warrant.
Do I have a reasonable expectation of privacy in my day-to-day activities based on where my cell phone is located. I certainly do not have a subjective expectation of privacy, and I certainly do not like knowing that I can be tracked. So the real question is whether society, through five justices, will find that we have a reasonable expectation of privacy.