[derndarn]

I have a 2009 Passion Cabriolet my alarm system has been giving me nightmares since just about new. Smart/Mercedes Benz dealer can not figure it out.
The alarm goes on all by itself. Please help

 

[jwight]

Welcome to SCoA!

Probably the interior motion sensor. Covered here: https://www.smartcarofamerica.com/threads/alarming-situation.6201/ Since your car is well out of warranty any repairs will be at your expense....

 

[colin555]

Yes, the most common problem on the 451 alarm is the sensitive cabin motion sensors, and best to disconnect them.

On the 453 alarm the most common problem is the hood (bonnet) switch, that no longer makes contact with the hood. it becomes spurious (contact opening and closing) and goes off any time when parked with sounder and side indicators flashing. Solution is to glue a plastic piece to the inside of the hood opposite the switch plunger to reduce the gap of the switch to hood, and that prevents the switch plunger becoming spurious. Interestingly even if you do not have the 453 alarm fitted, you do have the hood alarm switch and the same problem can occur when parked with a spurious alarm, but as there is no sounder there is no sound, but your side indicators flash as an alarm LOL.

 

[Bob Denman]

I was going to joke about "Who would steal one of these anyway?": but mine was stolen (and recovered); in it's previous life in NYC... ?