Up for grabs: A wireless home audio setup from Sonos, including two S5's ($399 each) and a ZonePlayer 90 ($349), which allow you to link up your entire digital music library with your existing components and Sonos' flawless speakers in every room without pesky cables. It's all free to a lucky reader who can spot the difference in this set of images. In each pair in this gallery there is one difference between the two images. To enter for a chance of winning, email all 8 answers to gimme(at)fastcompany.com with the subject line: Spotted The Difference (please note that only emails with the correct subject line will be eligible to win). The winner will be chosen randomly from the people with correct answers. Only one entry per IP address.

Sweepstakes Rules.

A collection of products designed by Dieter Rams.

T1000 Portable Radio, designed by Dieter Rams in 1969.

Buildings and construction sites in Dubai.

Millenium Park master plan in Chicago, Illinois, designed by architecture firm Skidmore, Owings & Merrill.

Pearl Academy of Fashion in Jaipur, India, designed by Morphogenesis, was named one of the 2009 World Architecture Festival winners.

TKTS booth in Times Square in New York City, another World Architecture Festival winner, designed by Perkins Eastman.

Obsolete telecommunications in the Baikonur Cosmodrome.

Clever packaging design for Hattomonkey milk cartons.

1. Email gimme(at)fastcompany.com by 11:59:59 p.m. EST on Friday, December 11, 2009 for a chance to win. Subject line must read: Spotted The Difference, to be eligible.

2. In your email include the slide (title) number and a brief description of the difference you spotted. (Hint: there's one difference per slide).

3. We'll select a random winner from the correct pool of entries on Monday.

Sweepstakes Rules.