A stingray is basically just a base station emulator, right? It should be theoretically easy to detect whether or not your phone is connected to one based on the output power setting on your phone's radio, and knowing the distance to the legitimate towers around you.
Since all phone adjust their power output to the minimum necessary to maintain a link to the base station, If the power setting on your phone is too low for the distance, there is a good chance you are connected to something much closer to you.
All we need is an app that knows where all of the towers are located (freely available information on the web) and that can make a reasonable calculation as to how much power should be required to maintain a link for a given phone position.
Any thoughts?