Pottermore will be the big selling point for Sony Reader Wi-Fi

Lightweight device will have a limited-edition version that comes with voucher to download first Harry Potter e-book.

Sony has unveiled its latest e-reader device, the Sony Reader Wi-Fi, and is hoping it will appeal to millions of Harry Potter fans this Christmas.

Why? A limited-edition version of the device will come with a voucher for fans to download the first Harry Potter e-book, when it is launched on J.K. Rowling's Pottermore website.

That's not the device's only selling point, of course. Sony claims that it is the "world's lightest 15.2cm e-reader", weighing in at 168 grams. Sony also says its touchscreen is an improvement on previous devices.

The Reader Wi-Fi will tie into Sony's Reader Store, and will also include a Public Library feature to borrow e-books from libraries in the UK, US and Canada. The device has 2GB of storage for e-books, and claims to go for three weeks at a time with its Wi-Fi switched on before needing a recharge.

The device will go on sale in Europe in October, although the Pottermore special edition may not be available in all countries.