If you have a fella who loves adventures reverse geocache box might be a great idea. You can set coordinates to some weird location where he could struggle to reach in order to open it. Renauld Schleck once found broken GPS watch and decided to make use of it. A reverse geocaching box seemed right idea since. And so he put a schematic out of STM32 microcontroller, GPS receiver, cell phone screen and locking mechanism made of laptop optical drive.
The box has a single push button. Once user switches on, device waits for GPS signal and once locked LCd displays how many meters it is located from objective and turns off. Once yo uare in right spot it reads and unlock box and then switches off. Since it is operating in such short periods it is enough power from clock battery which also hols pretty good power management circuit.
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