Foundation For Economic Education has the article The StingRay Is Exactly Why the 4th Amendment Was Written.
Police have the power to collect your location along with the numbers of your incoming and outgoing calls and intercept the content of call and text communication. They can do all of this without you ever knowing about it.
I was horrified to read this article. I wanted to do an independnt check of the veracity of this story. Rather than use the links in the aricle, I did my own Google search.
YouTube has the video How StingRay cellphone surveillance devices work from The Washigton Post.
The ACLU has the article Stingray Tracking Devices: Who’s Got Them?.
WikiPedia has this article Stingray phone tracker.
I am now convinced that this is a real threat.