[DLJ] The service manual says that when the security system goes off, *all three horns* sound, plus headlights up and blinking. I set one off inside the dealership once, and it was loud.
For home test– just lock up the car with the driver window down, wait until the security light next to the button on the driver’s door starts blinking. Then open the door, or pop the trunck via the switch on the door, or pop the engine cover.
Oh yes, to turn it off, you have to put the key in the ignition, and turn to the point where the warning lights come on.