While Apple recommends charging the Apple Watch every night, light sleepers with some battery life to spare might appreciate the alarm feature. As opposed to a typical alarm that wakes you up with noise, the alarm on the Apple Watch wakes you up via haptic feedback, simulating a gentle tap on your wrist. You might say that the Apple Watch alarm is ideal for those times when a nap is in order.
To set an alarm, simply select the Alarms app on the Apple Watch app screen. From there, firmly press the display, otherwise known as a Force Touch, tap "New" and then "Change Time." You can also set an alarm via Siri.