All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His Slave and Messenger.
If you mean that you switch off the alarm clock before you wake up completely so you continue sleeping and miss the prayer, then you should not put the alarm clock near you or within reach of your hand. If you put it far from you, you will not be able to switch it off unless you get up and move towards it, and accordingly you will wake up completely. You may use two alarm clocks if you sleep heavily or ask the Mu’aththin or some of your brothers who maintain offering the Fajr prayer in congregation to call you by phone, or use other means.
If you mean something else, please clarify it.
Allaah Knows best.