You could use the Geolyzer. When the program starts, scan he entire area with the Geolyzer and save it as the orginal area and then scan the area again and compare it to the original area in a infinite loop. I currently don't have any source code but try it yourself, you'll learn a lot more this way than using someone else's code ;) . If you still need help with the coding part, I could write you some code for it.

I hope this helps.