Google is in the midst of more than $120 million in construction projects at its Mountain View headquarters, including work on a series of new or previously secret hardware testing labs that hint at the Internet giant's expanding interest in crafting consumer devices like its rivals Apple and Microsoft.

Among the projects, revealed by a review of public records by this newspaper, are a lab to test a new consumer product under the brand name "@home" that will wirelessly stream music or data to other household devices, apparently similar to a prototype home audio service Google demonstrated publicly last year. And, most intriguingly, Google is modifying a lab for a project enigmatically named "Project X," which appears to involve precision optical technology and could be part of the secret technology projects Google co-founder Sergey Brin is heading.

The highest-profile project will be a "Google Experience Center" under construction at the core of the Googleplex. The 120,000-square-foot center will be a kind of private museum for Google's most important clients and partners, where the company plans "to share visionary ideas, and explore new ways of working" with up to 900 VIPs and other important guests, according to documents Google filed with the city of Mountain View.

"The Experience Center would not typically be open to the public -- consisting of invited groups, and guests whose interests will be as vast as Google's range of products, and often confidential," Andrew Burnett, an architect working on the project, explained in a letter late last year to Mountain View officials. "Therefore, the Experience Center must also operate somewhat like a museum, exhibit, or mercantile space allowing flexibility in the exhibits so that as Google's products and needs change, the space can adapt."

As Google becomes increasingly focused on selling its products to other companies, schools and government agencies,...