My buddy uses a big-ass knife switch on the battery + terminal, under the hood.
Since you have to open the car to 'pop' the hood, the only way to steal it is to get inside somehow (slim jim, smash the window, etc), pop the hood, pop the hood safety, know which black plastic box has the knife switch, open that, close the switch, close the hood, hotwire the ignition, and, finally... drive away.
Too much trouble. some other victim car will be chosen by the typical car thief.
That works on older cars, on newer cars they will run like shit if they are constantly killed. The ecu likes to learn things, the transmission ecu, the radio, all your settings. A knife switch on the fuel pump or starter would be better.
Since you have to open the car to 'pop' the hood, the only way to steal it is to get inside somehow (slim jim, smash the window, etc), pop the hood, pop the hood safety, know which black plastic box has the knife switch, open that, close the switch, close the hood, hotwire the ignition, and, finally... drive away.
Too much trouble. some other victim car will be chosen by the typical car thief.