The Apple Watch operating system, introduced in April 2015. In the same year, watchOS 2 added a variety of features, including an enhanced Siri, more watch faces, support for third-party apps that run without pairing to the iPhone and an alarm clock/nightstand mode. In 2016, a more efficient watchOS 3 debuted with Apple's second-generation smartwatches. New watch faces and several features were added, including more Siri integration, improved social apps and a personal alarm that dials an emergency number. See Apple Watch and Apple Watch Series 2.