The Miniature Pair of Pants was an invention that Danny created some time ago but never used on Chris. Chris found it while he wasn't talking to Danny, in Season 11. In the episode Secret of the Pants Chris found the invention when he was trying to get his lucky penny behind the fish tank. He reached down and grabbed something. Thinking it was the penny, he pulled it up, but it was actually the pants. They made him unconscious.
It was one of the only inventions the Construction Crew forgot to remove from the house.
The pants were able to teleport, bite (which it did, making Chris unconscious), walk on their own, fart and shoot lasers. When they get defeated, a giant glare is summoned around it and forces surround it. Then they explode.