Note: This information is only applicable to anti-theft alarm systems fitted as standard equipment by Mercedes-Benz.
Some models are equipped with an alarm system as standard equipment. The system has switches on all doors (including the trunk lid and tailgate), bonnet, audio unit and ignition switch, as well as a tilt sensor that is sensitive to impacts. If a door, trunk lid, bonnet is opened or the ignition or radio is turned on when the alarm is armed, or if the tilt sensor is triggered, the horns sound and the headlights flash. The system also has an immobiliser function that disables the ignition system / starter until the system is turned off.
The protection is activated using the key in the front door lock or in the trunk lid lock; on later models, the system is activated when the doors are locked using the central locking system. The LED in the center of the central console starts flashing, indicating that the anti-theft system is activated.
Note: On early models (released before September 1987) the protection system is enabled only with the help of the main (rectangular) key. If a secondary (round) key is used, the door will close but the anti-theft system will not be activated.
If the alarm system fails, please contact the Mercedes-Benz service station. Using a dedicated diagnostic tester, you can quickly identify a system malfunction.
Original source of information (mercedesman.ru)