JA asked:

“Couldn’t we just say we got the data by monitoring cell phones? No one would be the wiser.”

Ultimately, I think it’s important to keep the title of Wretchard’s essay in mind. This isn’t about a sensor. Nor about 2 or 3 new sensors, no matter how high-tech they may be. The real weapon is the software which integrates the sensors, which would be a database. Therefore, it’s not about a stream of data. It’s about the product of threading together multiple streams of data.