Alarm system keeps going off...

Hi
Just woken up for the 8th time to the sound of my Prius alarm system sounding.
It's an EU prius with the default alarm in it and every time it goes in for a service I tell them about the problem. They tell me they have lowered the activation threshold. I never notice any improvement.
A few questions
1. Is there any adjustable 'activation threshold' on the prius alarm system or are they just fobbing me off?
2. As I don't hold out much hope of the dealer solving the problem can anyone give me a checklist of things in order of likely-ness of what sets the alarm off.
3. I have pro-tem half solved the problem by removing the fuse that leads to the horn. However a second siren still sounds despite the horn not souding. Where is this siren speaker located as I intend to disconnect that too.
A few observations.
1. It is almost impossible to get the alarm to go off deliberty, such as by waving hands around inside the veh, trying door handles, rocking the veh, hitting the glass, etc. For that reason, I am not sure I believe therefore that it is an intermittent sensor issue as I have "banged every door" so-to-speak.
2. I have checked the battery level and while all the readings are a bit on the low side, ultimately all the results are within the recommended thresholds as defined elsewehre on this site. With that said the car is 4 years old, could the battery be malfunctioning in other ways?
3. Pressing the button under the steering column does not affect whether the alarm activates or not.
I feel like I have run out of things to check. Please please help me before I make an enemy of everybody on my street!!
Thanks v much.
iii