On Monday, at its Worldwide Developers Conference, Apple teased the upcoming release of the iPhone’s operating system, iOS 12. Among its most anticipated features are group FaceTime, Animoji, and a ruler app.

But iOS 12’s killer feature might be something that’s been rumored for a while and wasn’t discussed at Apple’s event. It’s called USB Restricted Mode, and Apple has been including it in some of the iOS beta releases since iOS 11.3.