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First it was tracking consumers. Look at the location histories that public transit agencies store (EZ-Pass, Metro Card, etc), not to mention credit card and cell companies that track and analyze consumer location info for the company's benefit. Money is the greatest motivator.
After these systems are set up, police realize that they can gain access and use them to track suspects or "terrorists." Once the capabilities are well-publicized, parents get interested and companies spew out spinoff consumer-friendly tracking tools... such as Verizon's Chaperone, which more average people buy... which LE will subsequently take advantage of...
Every new advance in location tracking technology is an exploitative cycle between the market forces, Big Brother and normal human attachments.
"We learn from history that we learn nothing from history." -- George Bernard Shaw