The Reverse Geocache Puzzle

The Reverse Geocache Puzzle | Arduiniana: "Early this summer, the friend who first introduced me to Arduino amazed us with the news that he was moving to France to get married. Once I recovered from the surprise, it occurred to me that putting together some sort of Arduino-based wedding present might be a uniquely fitting thanks for his years of friendship and for helping get me started in this delightful enterprise. And so after weighing several ideas — I didn’t fancy adding some ugly techno-junk to the pretty collection of tea cozies and china sets — I finally settled on building the device I describe here: a puzzle box that won’t open until it is taken to a certain location."