Ok, IMO audiovox is not a very good company, I think they sell stuff at Radio Shack don't they?? But that aside you have to figure out what you want your car alarm to do. I am sure people will think a lot less of me but when I was younger I used to break into cars ALOT. Reasons why I did this aside, I learned a lot about what ya want in a car alarm cause they often don't stop a thief very well. First off, I would say you want the alarm to have perimeter. Perimeter is kind of a beam around the car that will warn people to step back (or not if you dont want it too) and most importantly it will tell the car if lets say a window is broken. This is very important because many people don't have this so nothing stops the person from just breaking your window and climbing through w/o opening the door or hood and simply removing your system that way.
Next, you have to decide where you want your "trip" pins. These pins basically are wired into the alarm and tell it if they are triggered. I think of them working kind of like a trip wire or something for a claymore. Anyway, you want at least 1-2 under your hood. If you dont have one under there someone could get your hood open and disconnect your battery and then your alarm is worthless. This is especially important if your battery can be gotten to easily through a grill or from underneath the car. Next I would put a pin in the trunk and maybe one in each door if possible. That way if for some reason the perimeter doesn't work and someone opens the door the alarm will go off.
Last thing you could do if you were real serious, which a friend of mine did, is hook up a 2nd battery in the car. Run the alarm off that battery. Most thiefs won't expect this so after they disconnect your battery from underneath or however they will pop the lock open the door and still set off your alarm. Plus you could then have a pin to trigger the alarm when the door opens and/or the perimeter will go off.
I would also remember this, if you leave your alarm on and you have it set up to tell people to step away or if it is set to be to sensitive to vibration or whatever this is really going to annoy people. After they get annoyed and nobody pays attention to your car people will kick it and key it and stuff like that. So I would not have that on there and just put a nice bright LED in the car so people know it has an alarm. Your average run of the mill punk will pass on it and they are the usual perpetrators. So I guess after this epic response what I'm trying to say is get an alarm that you can add trip pins and stuff where you want them, have it professionally installed and you should be good to go. Most Viper alarms can do just about anything, even be hooked up to a pager. (Yeah its been a while but I'm sure I know more than the average guy still)
Keep in mind that no matter what you do though, if someone wants your car they will get it. This guy I know had an award winning alarm set up in Minneapolis. He had everything, the extra battery and all that shit. Well someone got their hands on a flat bed and pulled up to his new car and hauled it up. So what would you think if you saw a newer car getting towed away and the car alarm was going off? You'd probably think they skipped their car payment and laugh.
