Mikal Hart’s original “reverse geocache” puzzle ended up making a big splash when we first posted about it last October. Now Russ Weeks has produced his own version using an Arduino, an HD44780 display, a servo, and an EM406 GPS. Like Mikal’s version, Russ’s puzzle will only open in one particular location on the surface of the Earth. If it’s elsewhere, pushing the button just gives a readout of the linear distance to the location it wants.