How to determine if your vehicle is equipped with an OEM factory installed alarm system:
Step A: Roll down the driver’s door window: OEM alarms are set one of three ways depending on the model of vehicle:
#1 Close all vehicle’s doors and lock the doors using the factory remote or #2 press the power door lock switch in the vehicle while the driver’s door is open then close the door or #3 close the driver’s door and turn the driver’s door key cylinder to the lock position with a key.
Step B: After locking the vehicle's doors using one of the three procedures above, wait at least 1 minute then reach in through the open window and manually open the driver’s door from the inside (some vehicles may require pressing the power unlock switch first). If the vehicle is equipped with a factory alarm system the vehicle’s horn will start pulsing all most immediately after the driver’s door is opened.