It's exam season, and that means that students suddenly feel the need to tidy their room, do the washing up, or anything else to avoid sitting down and actually doing some revision.

Well, now they can be kept in place until it's time for a break. The "Study Ball" is a whopping great big 10kg ball and chain that attaches to the ankle of the student in question. It's equipped with a timer that allows a person freedom after a set amount of time - shown on an LED display.

"For security reasons", says the creator, designer Emilio Alarcón, "Study Ball may not be programmed for more than 4 straight hours of study time". There's also a safety key that'll let you open the manacle before time is up.

It's made of steel, and powered by three triple-A batteries. The chain is 42cm long. It costs £77, but at the time of writing it's displayed as "Not available" on the website. We've contacted the sellers to ask when it'll be for sale again, so check back for updates.