I've given up on alarms
I've had at least 3 different alarms put in my car and I'm convinced my electrical sh*t is just wiggy. The alarm will go off for no reason at all.. all the time or it wont go off if you pound on the doors/windows etc. More headache than its worth.
What I do suggest that is inexpensive is that club for the brake.. I forget what its called but you fasten it around the brake pedal and it is impossible to step on the brake or cut the brake since its made out of steel or whatever. If you cant step on the brake, you cant steal the car, you'll end up wrecking it.