It's not what you think!
Each person called is on a watch list of some kind, there are literally thousands of different kinds, and they use this technique to pin point location, capture video of you picking up your phone or even capturing your digital voice or image to add to their data base.
There are literally thousands of different "pieces of data" a single call can generate.
It's nothing to be concerned about and in fact it's actually where a tremendous amount of the trillion dollars of unaccounted for "black budget" dollars goes to each year.
The reason this country is safe is because a few million men and women are tirelessly watching and listening, checking and rechecking, on people like you and me!
So if you receive a call like this, just know in your heart, they are looking out for you and say a quiet and sincere thank you!
Bob