A new Bloomberg report reveals that Apple has allowed some companies, including Facebook and BMW, into its Cupertino headquarters to test apps that will be released alongside the Apple Watch. The report describes the secretive and tightly controlled process of working with the wearable — internet access is blocked, and developers cannot bring outside materials into the room that houses the Apple Watch.

Bloomberg reports that developers are sometimes forced to share a room to work on the watch, and have to leave the code for apps in development on hard drives that can't leave Apple's offices. So strict are Apple's rules that it will only send the finalized versions of apps developed by third parties to their creators closer to the device's launch. Stephen Gates, vice president of Starwood Hotels & Resorts Worldwide, visited Apple's headquarters to develop software that would let wearers unlock hotel doors. "There's a lot of confidentiality," Gates said, but he didn't elaborate on what specifically happened during his trips. Bloomberg notes that developer guidelines suggest apps be used no longer than 10 seconds at a time.

The companies allowed this close access to the watch have been working on a range of apps ahead of Apple's event on March 9th. In September, BMW said its Apple Watch app would be able to track an electric car's battery charging status, while Tim Cook said other apps will be able to help people find their cars in parking lots. The Facebook-owned Instagram is developing an app that will use the watch to notify wearers when chosen users of the photo-sharing app post pictures, and let them scan through images from their wrists.