For some odd reason, the current software builds of the Xperia XZ Premium and Xperia XZs do not feature either double tap to wake/sleep functionality. We’re not sure why Sony would remove this functionality on its flagship devices, but we’re hoping this is a temporary issue that Sony will fix in an upcoming update. Tap to wake is a pretty fundamental feature in smartphones these days, so we’ll keep you posted if and when tap to wake returns.