I don't get how fitting the legendary warning gongs from the sunken city of Leshp will help when the alarm fails to register someone sticking their upper torso through an open window
Yes an upgrade would be ideal but nailing sirens on isn't overly difficult
To plagiarise an old saying
I don't need to make my car the most secure in the world. It just needs to be more secure than yours
If a true professional wants your car they will take it
So all you really need to do is deter the scrotes who know that nicking a BMW is easy coz they seen it on YouTube innit bruv. If the alarm goes off and the nick-a-bimmer.com kit don't work they will foxtrot oscar likely as not