Databases can correlate location data from smartphones , the growing number of private cameras, license plate readers on police cruisers and toll roads, and facial recognition technology , so if law enforcement wants to track where you are and where you’ve been, they can. They need a warrant to use cellphone search equipment: Connecting your device to a mobile device forensic tool lets them extract and analyze all your data if they have a warrant .

However, private data brokers also track this kind of data and help surveil citizens – without a warrant. There is a large market for personal data, compiled from information people volunteer, information people unwittingly yield – for example, via mobile apps – and information that is stolen in data breaches. Among the customers for this largely unregulated data are federal, state and local law enforcement agencies .

Surveillance is pervasive: Yes, you are being watched, even if no one is looking for you