Adding Alarm Sirens

[Kace]

I am planning to slightly upgrade my current alarm / immobiliser and want to make it uncomfortable for someone if they gain access to my boot. I am planning to install a couple of additional loud sirens / horns inside the boot which will be triggered by my current alarm.

I was planning to access the current alarm siren under the bonnet, disconnect it and reconnect my additional sirens in parallel with this one, so that they are all then triggered simultaneously.

Anyone here upgraded a standard alarm in this way by adding some siren horsepower in the cabin, engine bay or boot ? I may be oversimplifying the job so looking for handy advice.