The stock alarm comes with a security system that will go off only if the car door is opened. The intruder could break the window and enter the car that way and the alarm would not go off. Or the car could be towed away and disassembled at another location.

There are companies that offer complementary security that works with the stock system for shock.

I paid for the extra alarm and adjusted the sensitivity for my own personal taste. The alarm has only gone off 2x since I've parked it, and I think it was because of the location in the garage where I parked my vehicle.

My motion sensor will chirp 5x if you bump the car mildly and 1 minute if you hit the car with too much force.