starshine

I've set the horn to sound when I lock my C220 Bluetec - but the horn is now exhibiting odd behaviour, and I can't work out whether it's a fault or a safety feature.

If I decide to leave the car for a moment, engine running, transmission in park, as soon as I'm half way out of the vehicle, the horn sounds for moment.

I can't find anything about this in the manual.

Is this a fault... or meant to be some sort of warning?