Alarm issue

[rossman-abz]

Hi people
I bought a 66 plate cls shooting brake earlier this year and last weekend I left the rear window open and the alarm didn't activate. It was a very calm night which is very rare in the north east coast of Scotland. Would this explain why the alarm didn't go off, or is this a fault in the alarm ?
Just want some advice from you lot ( the experts) before I go into the dealership dummy's.
Thanks in advance.

It's a truly beautiful car

 

[markmifsud]

I think the alarm will need more than just a window to be open to set the alarm off, ie some real activity inside the car.

I can leave my roof down all day without any alerts.