I had a neighbor once that had a really hard time waking up. He would set his alarm for 4 AM for his 8 AM wake up. He would sleep through 4 straight hours of his alarm. It was a real problem for him. He had lost a few jobs because of repeated tardiness and was really at the end of his rope.
He tried the bed shaker, he tried a wrist watch that vibrated, he tried bright light alarm clocks, and nothing worked for him.
Being the kind an benevolent neighbor I was, and knowing his plight, I gave him a screaming meanie 220. A few days later he thanked me with a fruit basket (Who doesn't like food?!) He never slept through his alarm again! He even took it with him when he traveled. He was able to set the alarm for the exact time he needed to get up, and no longer had a 4 hour marathon alarm clock session.
If you have trouble waking up, or know someone who does, why not get a screaming meanie? Do you have a teenager that won't wake up? Collage student craming all night for a final in the morning? Work the graveyard shift? This alarm might be right for you.