Stay away from a factory alarm. They are useless. You are better off with a quality after market alarm.
If you do go after market make sure you talk to the installer to install a back up battery. In case the thieves short circuit the main battery or manage to cut wires.

One other notable you can do as well. I also have an in car camera that records an event if the alarm is triggered. I had this on my last car and worked like a charm. I caught the person breaking into my car with video footage. The video footage was then given to the police and three days later the person was caught. Apparently this guy was stealing property from a few cars in the neighborhood.

Either way good luck!