Detection would not matter. The armed forces have been gutted of real Americans in top leadership positions, so We The People would never know they were coming. By the time a few real American junior officers went rogue and disclosed the invasion it would be too late.
Read this, if you haven’t already:
What Good Can a Handgun Do Against An Army?
http://www.freerepublic.com/focus/f-backroom/2312894/posts