“One example is how Amazon.com provides free gift wrapping in order to help track which books are purchased as gifts. At one point Amazon was not tracking the number of items sold as gifts; the company added the gift-wrapping feature to be able to track it. Another example is how consumers are given coupons so retailers can see, among other things, what newspapers their customers read. Inexpensive personal sensors and apps for smart devices are available for many types of measurement about human activity.”