Help with designing security.

 I have the following ideas for designing my security system, I don't need it to be fancy and super elaborate, just something that will do it's job and give the theif a bad day.(Note: I am not a theif nor have i ever stolen a car, nor to I assume to know anything about what a theif does, this is my own assumptions.)

Time line of a car theift (at least what I think it would be)

second 0: Guy smashes drive side glass, pops door open.

second 1: Alarm goes off, guy has his head under dash looking for the brain.

second 2-3 maybe 4: Finds the brain, cuts the wires. To his surprise the alarm is still sounding, he has found a decoy brain, and has lost some time. He searches a little more for the real brain, which is burned either in the center console, behind the gauge bazel, behind the center vents or behind the glove compartment.

second 5-6: Not finding the brain he pops the hood and races around to pull fuse / battery negative. The alarm still sounds (thanks to batterback up on brain and all sirens.) At this point he has a choice, run or smash the external siren in hopes of quieting the alarm. Lets say he goes the smashy smashy route.  (note at the 5 second mark from when the alarm first started sounding, two 130+db siren buried in the dash begin to sound, making any work in the cabin nice and painful if not annoying.

second 6+: seaches franticly for the brain, or decides to hot wire the car, no go, there is a fuel cutoff in addition to a starter cut off.

At this point the interior sirens are still attracking attention and making his life miserable. You think he'd quit?

So what are you asking us for ? A system that can do all this or an installer that can do all this ?

  Well what I REALLY need help with is finding batter backup sirens and a circuit to make the 5 second delay happen.