With Christmas coming up, people will soon be putting gifts under the tree, to be opened on the 25th. Of course, curious minds will go to work, trying to figure just what is in those packages. You can only tell so much by simply looking at a box, but feeling its weight and shaking it can provide additional clues. If you want to really surprise those box-shakers, here’s a fun way to do so.

This Instructables guide walks you though the process of using a small sound recording unit, and configuring it to go off when shaken. You only need a few inexpensive parts and a glue gun. Once you have it rigged up, just record an amusing sound, and put it in the box. Wrap your gift, and wait for someone to come along and shake it.