The $115 Study Ball weighs about 20 pounds, which makes it difficult to get up and stroll out into the prison yard while wearing it. Fortunately, the gadget comes with a safety key that can open the shackle at any time--a welcome feature if the wearer needs to take a bathroom break. Also fortunate: the device can't be programmed for more than four straight hours.

The Study Ball was created for gifts site Curiosite by Spanish designer Emilio Alarcon. The project was born of a conversation Alarcon had with a friend who was studying for a civil service exam and said: "I haven't left the house in a week, this is like being in jail."

Beyond use on teenagers, Curiosite also recommends the ball and chain for Web designers, computer programmers, bloggers, architects, translators, and anyone else who spends long hours sitting in front of the computer. Please note that once it comes off, wearers are required to pound out a few license plates.