Baltimore Police Surveillance
Article: [URL]http://baltimore.cbslocal.com/2015/04/08/baltimore-police-often-surveil-cellphones-amid-us-secrecy/[/URL].
When in use, authorities record that a transmitting device (cell phone) is in the area. Feds have 'social networking' software that associates one number with another based on the number of times recorded simultaneously in a cell. Apps such as burner and hushed offer no protection. Although use of this technology against this behavior is purely speculative, license plate readers are common and pervasive.
Article: [URL]http://cnsmaryland.org/2014/02/12/maryland-license-plate-recognition-networks-prompt-state-federal-concerns/[/URL].
I recall an 'old crow' saying: "If you have thought about it, we have done it. If you have heard about it, then it is obsolete. ".
Be safe.