Geocaching is a hobby that combines the fun of a scavenger hunt with modern GPS technology. One party will hide a small cache somewhere, then post the general location and the exact GPS coordinates for other parties to find. The goal is to use GPS navigation to find the hidden cache. Often, people will sign a log or leave a small memento in the cache for others to find. Trent Wyatt took that idea and flipped it with this “reverse geocache box” that will only open when someone takes it to a specific GPS location.
Wyatt designed this with gift-giving in mind. The box has an internal lock that isn’t accessible from the outside. The only way for the recipient to open the box and get their gift is by pushing the red button when they are at the location set by the giver. If they aren’t at the proper location, the display on the box will show the distance to the proper GPS location and how many tries they have left. The idea is that the giver will tell the recipient the general location and the recipient will have to perform triangulation to find the exact coordinates where the box will open.
If you want to build your own Reverse Geocache Box, you can start with a hinged wooden box. You can then use any Arduino board (like an Uno or Nano) to monitor the box’s location through a serial GPS module. Before locking up the box, you will need to add the unlocking location to the Arduino sketch. When the box closes, the Arduino locks the lid using a simple servo-actuated mechanism. Power comes from a pair of 18650 lithium batteries through a 5V regulator. Distance data displays on a small 16×2 character LCD screen. You also have the option to add a small amplifier and speaker to add sound effects (like a celebration tune). You can, of course, include a secret backdoor to open the box in the event that something goes wrong.