Your natural clock is quite strong . Basically you set a subconscious intention to wake up everytime you set a alarm , if the intention is strong you internal clock will wake you up at the time of alarm . to be honest , I think natural awakenings are the "softest" way to wake up , like even if you wake up by an vibration alarm it would still be just as hard to fall asleep as it is without an alarm and likely even harder (imo) .

If you think you are having trouble sleeping just set an alarm earlier in the night so you get less sleep and are more tired