James writes in with this fun project he made to help him find his tent at a festival. I like the way he interfaced his indicator beacon to the cell phone. When the phone gets an incoming call, it lights up the screen, so he mounted a photoresistor right next to it. This allowed him to build a very simple analog circuit to control the whole thing. Nice hack!
If you used a pay-as-you phone for this, and hung up after a couple rings, it seems like this could be a really economical way to go.
This is what the completed project looks like: