Guests encounter a 3-foot Christmas tree decorated in colored lights. Green letters are scrawled one at a time to form a message. The words arrive slowly:
Ho Ho Ho The Mad Wrapper says hang your ornament here
Under the tree lay identically wrapped packages. The only thing unique about each is hidden within some electronics built into the ornament taped to it. When one of these ornaments is hung on a hook on the lighted tree the colors change and a new message begins. This one spells out a person’s name thus revealing the inheritor of the gift.
For a detailed discussion on how to build this take a look at Instructables: Arduino Controlled Message in a Christmas Tree