This a is a leprechaun trap. The Keep Out sign is to appeal to their mischievous nature. The shiny tin foil is to lure them in. They see the quarter, pull it, the string pulls the pencil, the box drops down.
You've caught a leprechaun!
At least that's how it's supposed to work in theory.
This is what we woke up to this morning. Those leprechauns are smart!