If you read about the stingray above, it's pretty easy to see why law enforcement wouldn't want it to be known - it should require a warrant. The fact that someone can intercept your cell signal without a warrant is garbage in my opinion. As the article says, it comes out "because terrorism!!" and then you find out that a given department (and probably all) are just using it all over the place for stuff that has nothing to do with terrorism. Presumably whatever things allow the department to seize property and money.