Siri has since been an integral part of Apple's products, having been adapted into other hardware devices including newer iPhone models, iPad, iPod Touch, Mac, AirPods, Apple TV, and HomePod. Two months later, Apple acquired it and integrated into iPhone 4S at its release on 4 October, 2011, removing the separate app from the iOS App Store. Siri was released as an app for iOS in February 2010. Its original American, British and Australian voice actors recorded their respective voices around 2005, unaware of the recordings' eventual usage. Its speech recognition engine was provided by Nuance Communications, and it uses advanced machine learning technologies to function. Siri is a spin-off from a project developed by the SRI International Artificial Intelligence Center. With continued use, it adapts to users' individual language usages, searches and preferences, returning individualized results. It uses voice queries, gesture based control, focus-tracking and a natural-language user interface to answer questions, make recommendations, and perform actions by delegating requests to a set of Internet services. Siri ( / ˈ s ɪr i/ SEER-ee) is a virtual assistant that is part of Apple Inc.'s iOS, iPadOS, watchOS, macOS, tvOS, and audioOS operating systems.