Common alarm clocks ignore your sleep cycles, they wake you on schedule no matter your are currently in your deep sleep. Waking up from deep sleep is unpleasant, it makes you tired and it may negatively affect your productivity during the whole day.
Sleep as Android is different. It tracks your sleep to find the optimal moment for your wake up. Waking up in light sleep is natural, gentle and it may only be compared to the experience of waking up without any alarm clock.
