Speed as a consideration.
You say that it will be faster to get to than a flashlight or pepper spray, but my question is this:
Will you be sleeping with the weapon in your hand? If you do not, then I don't see any advantage in speed of empoyment, and if that is a consideration, sleep with the flashlight in your hand
A good light will light up a room and even a PCP junkie can't see with 1/2 million candlepower in his face.
This idea just seems improper and, to a point, dangerous. If you fire that first blank and he doesn't run, he will be firing the next, and it more than likely will NOT be a blank.
Although you can see lots of advertisements for blank/metallic/movie-type guns in the back of many major gun rags, I would like to remind you that each round fired, blank or otherwise, has a certain amount of liability attached to it.
Unless you live in the boonies, it is probably illegal to fire a round at all, blank or otherwise. Most urban areas I have been to have laws prohibiting the discharge of firearms in city limits, save in defense of your life/property, and even then, you will be cited for it. Most likely even with blanks.
I would highly recommend that you not follow through with this. It may also be adviseable to seek some professional firearms instruction, both tactical/practical and legal/liability.
"I won't be wronged, I won't be insulted, and I won't be laid a hand on. I don't do these things to others and I expect the same from them." - John Wayne