The Proposal Box stays locked, hiding its contents—that is, until you bring it to a specific place on Earth. Once you reach that location, the latch will spring open automatically, revealing what’s inside.
The box has a simple interface; a single button and an LCD screen. The button turns the unit on or off, and the screen reads out how far you are (in miles) away from your goal. Just walk around until the numbers start going down, and when you hit the right spot, you’ll finally be able to see what it contains. (In case of emergency, or if you can’t reach your goal, there’s a failsafe mode: connect the two screws on the back of the box with a short wire, and the latch will pop open immediately.)
I used this to propose to my wife by leading her back to the site of our first date, a 20-minute walk from where we now live. Once I gave her the box, we strolled around the neighborhood where we met, and as the distance slowly counted down, we meandered towards the 150-year old (and now sadly defunct) pub where we shared a meal after a nearby bluegrass show. When we arrived, the box flashed one of the most important messages of my life, and with a short whirr, unlocked itself to reveal her ring.
Spoiler: she said yes.