A way to substantially reduce the cost is to use the little magnetic door switches that are used for alarm systems. They are only a few dollars, are very light and can be mounted with double stick tape so no holes are drilled in the dorm room. By the look of the prox switch it is something that you had lying around so use what you have but if buying new look for it.
Tools for Treasure HuntsView Instructable »
I have found that if you were to want to be completely evil you could make a stack of these wheels and place them in the treasure hunt. In the characters on the wheel place a word or a series of symbols that would identify that one wheel different to the others. The codes could change at every clue. This is just the basic hardware of the thing. Use your artistry and make it spectacular! If you a make it, please share as I am actively making a treasure hunt and could use all the ideas that I can get on this front.
Geared Code WheelView Instructable »
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Treasure hunt for adults (c...View Instructable »
I agree for the standard scrawl to remind myself of the cat or the groceries this is a bit cumbersome. But for that special touch it's a tool in my bag to make the wife go awww. That and I use them for my treasure hunts to print clues on and stick to things.
or more specifically lcd.print(f("blah blah"));
Most of the Serial.prints I commented out when I was getting toward the end of the build. Would that work for the lcd.print("blah blah"); ?
How to print on a post it noteView Instructable »
Arduino Treasure HuntView Instructable »