Arduino forum member RickP posted his awesome-looking reverse geocache box, which unlocks to reveal its contents only when it’s in a certain place on the globe. He uses an Arduino, a GPS sensor, and a trio of nixie tubes, which indicate the box’s distance from that special spot. When the button is pressed in that spot, a servo motor unlatches the lid.
The large amount of power drawn by the nixie tubes had to be taken into careful consideration. With four D-cell batteries, Rick estimates that the box can do 600 GPS fixes before they run out. Connected to the power button is a latching relay, which allows the Arduino to shut the power off after the GPS fix has been attained and distance has been displayed.
The enclosure is made from a French army medical box. And those guard rails? They’re Ikea drawer pulls.