> If you live in the rest of the United States, which is spread out and some quite rural, a car alarm can quickly notify you someone is messing with your car.

That really depends if you're close enough to the car, or in a building that makes it easy to hear noises coming from a parking lot. If I go to a mall or a big box store, I'm not going to hear my car alarm going off and other people are going to largely ignore it (since they've experienced so many false alarms in the past).

Car alarm systems should be silent and sent an alert to your phone so that you know someone is doing something to your vehicle and can check on it in a timely fashion.