watchOS 1 is the first release of watchOS, shipped April 24, 2015, on the original Apple Watch. Third-party "apps" were WatchKit extensions running on the paired iPhone with the watch as a remote display — an architecture chosen for battery and schedule that made launches painfully slow — while glances, actionable notifications, Digital Touch sketches, and the honeycomb home screen defined the first-year experience.

Watch faces with complications; glances; Digital Touch; Activity rings and Workout; Apple Pay on the wrist; Siri; and phone-dependent WatchKit apps.

watchOS 1 launched the wearable platform and taught its first hard lesson — remote-display apps don't work — answered within months by watchOS 2's native runtime. The Activity rings it introduced remain Apple's most durable fitness iconography.