For my 1989 300 E! Old vacuum system with alarm!


Alarm system is activated and deactivated when using the key in any on the locks. If your car has an alarm system from this time era, the key with a RED Sensor on it will arm and disarm the alarm system. If you lock the car without the key from the passenger door or with a keyless alarm system like the Viper, it will lock the car but without the alarm system! That is why when you unlock the car, the alarm will not go not go off. Unlock the car when it was locked with the key (thus activating the alarm) with the keyless system and guess what, the alarm goes off! Not a big issue for me! I can occasionally lock the car with the key in those situations where an alarm system might be helpful.

Big Dog, very interesting.
Mine is a '91 S-class, so should be similar.
What do you mean by Red sensor on the key: RF ID? coded resistor?
My keys appear to have no RF or resistor chips, or any embedded electronics.
But I guess it could be hidden under the rubber end.
I assumed it had no such system.
I'll try the push-button right-hand locking and see if it triggers the alarm.

This is getting interesting; makes me want to pull the door lock and see what-all they have in there. I know it's not too simple, because if you try to push the driver lock down, with the door open, it won't go down - so it's pretty smart.

DG

I always thought that the keys with the red dot on them were simply the master keys for the car, and had no other special significance.

However, none of my original W124 keys had the red dot on them and when I ordered a new set of locks and keys, none of the new keys had a red dot on them either.

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Steven Harrison

1993 300E2.8 - 196K
2001 E320 4MATIC - 86K

Here is a picture from page 30 of my owner's manual which is self-emplanatory. I have two keys and both have the RED sensor on it.

Picture quality not the best. Second paragraph reads: Vehicles equipped with the anti-theft alarm system are identified by having a red dot on the master, valet and flat keys.

Hope this helps!

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