Well an aftermarket alarm system will do if equipped properlyCare to elaborate?
If the crooks want your car they are going to get it regardless of what you do. They can pull a tow truck up to your car and just load it up and away it goes. I am not sure about how much reduction in your premium for having a better security system.Immobiliser is not good enough protection see here:
Also you will pay less for insurance if you have GPS tracking system.