Goddaym! You paid $500 for an alarm similar to mine? I paid $100 for mine. It even came with power window module. I bought mine from somebody else who gave up trying to install it tho. My friend and I installed it 1 hour tops.... ha ha.
It's crazy these days man. I've seen cars that got broken into and their alarm system got stolen also!
Anyway to run another siren, just get an air horn or another siren from an auto parts store and tap it from the original siren. It's the same as putting another speaker in your car. All you need is the signal. Tap it the same way......