It is very stressful on your body to be suddenly jolted awake. If you are regularly getting enough sleep, an alarm may even be unnecessary.
Alternatives include a sun alarm clock, which wakes you up by gradually increasing the intensity of light, thereby simulating sunrise, or a talking alarm clock, designed for the visually impaired.
I use the talking clock, as it allows me to sleep in complete darkness. If I need to know the time, I just press a large button, and the clock audibly tells me the time.1Sleep — Why You Need It and 50 Ways to Improve It