mbarrad

I STFF and could find no reasoning about this.

The battery in my smartkey ran out today and I could not open the doors remotely. I took out my mechanical key and proceeded to unlock the drivers side door. Upon doing this, the alarm went off. After researching this issue thinking it was a malfunction, I came across the part in the manual where it says that this is normal. I am happy that this is not a malfunction, but confused as to why Mercedes added this feature. The manual did not explain the reason behind this feature. I can't think of any logical answer for this. Would any of you know why the alarm goes off when using the mechanical key? A forum search yealded zero answers. Thanks guys.

BavarianPride

If i'm not mistaken, it's not your mechanical key thet sets of the alarm,
it's when you open the door the alarm trips.
the reason for this is, your remote key is dead and does not disarm your vehicle.
It prevents any one from entering your vehicle,by bypassing your door locks, without the alarm sounding and disabling the vehicle from starting.
Your mechanical key has no ability to turn off the alarm.
Once you put your key in the ignition the alarm will silence.
I hope this makes some sence, T.

GDawgC220

its sort of like someone using a slimjim to unlock your doors to get inside the car. Think of a tow truck driver, they use tools to unlock your car, same idea as the key. It doesn't disable the alarm system itself, just the door lock. Once that circuit is broken when the door opens, since its still active, the alarm will go off. It can't tell the difference between you or the tow operator or a thief trying to get in. The only way it can tell its you is the use of the remote.

Matt@Revolution

Another possible answer is that Mercedes is just getting cheap. Older cars with keyless entry also had sensors on the door lock tumbler that would disable the alarm when the key was turned in the door. As the new keys have the same secirity type cut to them which makes the tumblers very hard to pick, I don't see any real reason not to have extra sensors on the tumblers other than cost.

BKLYN_C

when you use valet parking or anything elese of that kind lock the glove compartment and leave the transmitter key with the cak, The blade key remains on the key chain with you.

mbarrad

Thanks Guys. That makes sense a little... I hope to get a new battery soon.

RES

Get two and put an extra in the glove box. Now that I know I might do that.

GDawgC220

Keys are around $200-250 each depending on the dealer, that's a lot of extra change just to throw in the glovebox :p

yeloaw

I think he's refering to the battery

valdes

Dealers also charge that for a battery

ScottW911

You can buy the battery at any CVS or Grocery store for a few bucks.