I'm confused. iPhones have an alarm clock already, and you can already set it to vibrate. Why do I need this app?

(Serious question. I'm hard of hearing, and I do this with my iPhone already.)

To answer some other questions I see in the thread, they make alarm clocks and doorbells specifically for deaf people. I personally own an alarm clock that has an attachment that you slip under the mattress. The vibrations from the attachment shake the bed, waking me up. I don't use it anymore, since I share the bed with my girlfriend, but it worked wonders for me in college.

Here's a website with some deaf-centric things like alarm clocks and doorbells: http://www.harriscomm.com/