This app shows if you are inside former east or west Berlin, in which historical occupying sector you are and how far you are away from the border...

It offers plenty of information about The Berlin Wall, former border crossings, important historical sites and leftovers of the wall all around the globe..

Also, a homescreen widget shows at a quick glance in which former sector you are in.

Get it here:

https://market.android.com/details?id=coboltforge.sw.thewall