The one with the hook is for your tow away alarm. It automatically is always on. When you turn your car off and lock it it's automatically activated. Look through the window and you should see a red light on the switch blinking. What this does is in the event your car is lifted while locked and closed from either the front or rear end the alarm will sound Letting you know your car is being towed. There is a way to turn this off. You push the button towards the off position and it will blink once then lock your car and look through the window the light should not blink that means the anti-tow alarm is off. Remember to turn this feature off when the car is being towed by someone you're aware of or the alarm will sound.
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Read this above it gives you a more detailed description of this feature.