Android Apps: You Name 'Em, I Build 'Em

Can you build a spotted app?
It would pick up another forum person within spotting distance (near enough to hear a DAS request) and emit a ringtone/vibrate.
It would collate data of spots across london, a spot density map (like a crime density map)

It would be interesting to find out where the most spots are and how this changes over time. Some bar charts would be good.

Feasable app?

Imagine of you'd built the app I asked for @benjam. You could have sold it to the govornmemt for £120 million