From the home screen of the watch, swipe LEFT to access 'Activity'➡ 'Activity Settings'. Tap 'Activity Settings' to set 'auto pause', 'heart rate alert', 'pace alert', and 'distance alert'.
Auto Pause: When auto pause is enabled, watch will automatically pause when you are resting or stop moving during your activity.
Heart Rate Alert: You can set a value to make the watch alert you when your heart rate jumps above the value you set.
Pace Alert: You can set a target pace to make the watch alert you when your pace is below the target pace.
Distance Alert: You can set the desired distance to alert you. (eg: vibration at each mile)