According to a report by technology website Mashable, a quick tap or touch between the thumb and forefinger of the wrist wearing the watch will answer or cancel the phone call. No need to touch the clock for that.
The function of the feature can be defined through the app. It can turn off the timer, snooze the alarm or pause the song. The Apple Watch understands the user's double tap gesture through different readings.
About the feature, Apple said in a press release, the double tap feature is activated by the fast neural engine of the Apple Watch Series 9. Coupled with new machine learning algorithms, the engine processes data from the accelerometer, gyroscope and optical heart sensor. The algorithm detects small wrist movements and blood flow during a double tap of the thumb and index finger.