I dont think the write up for the alarm in the manual is correct, as my does not have a shock sensor, yet it show's it in the manual.
Anyway, as for the alarm sounding after the car is locked it could be something like a slight power surge setting it off, for instance I have LED side lights that flicker on/off when i lock the car and sometimes i've noticed that they stay very slightly illuminated for around a minute or so, even though its not affecting the alarm at the moment, it probably could do .
Do you have a "smelly" dangling from your mirror, this is another common thing for setting of the sensor, i've also known a slight breeze through the air vents to trigger an alarm.
Does it trigger night and day, it could be something to do with your light settings ie, the "see me home" setting where the lights stay on for a little while, basicaly try to elimate things so that you can pass this all to the dealer if you need to take it in.
intermittent problems like this are a pain to pin point.
Ps, i recently had a problem with the central locking on my RCZ, (boot opening by itself when unlocking the doors) when it went into the dealers they couldnt find a problem, as it had righted itself, typical ! However the service manager did comment that they had seen a couple of models including the RCZ where the central locking and the alarm system needed re-setting due to locking and false alarming issues. might be worth speaking to your dealer ?
