Police across the U.S. can now buy a map of where your phone has been without a warrant, which is bad news for anyone who uses free apps.

• A company called Fog Data Science sells police a searchable database of phone locations pulled from ordinary weather, shopping, and navigation apps.
• For the price of a used police car, a small-town sheriff can draw a box on a map and see every phone that was there, plus three months of where those phones went next.
• It is legal because of a 1970s rule: once you hand data to a company, courts say it is no longer private, so the government can just buy it.
• The "anonymous" label is meaningless — a device that sits at one address every night reveals a home, and a property record turns that into a name.
• The same pipeline has already exposed a senior U.S. Catholic official, wrongly pulled innocent people into murder and burglary cases, and leaked location records for devices inside military bases when a broker was hacked.

Outlook: The Supreme Court ruled in June that geofence searches count as searches, but nothing stops agencies from simply buying the same data, and Congress has not passed a law to close that gap.