some work off the ignition switch and also the door switches so when you get out the alarm automaticly turns on. this is called passive arming... and is normal only found on expensive alarms......... i have a cat 1 laserline and i know its an anoying problem of which with mine being a cat 1 i cant do anything about it...............
if gemini dont know........... then alls i can suggest is that you find a local or any gemini alarm fitter of which they will have fitted loads of theses and will know how they work...........
but like i say if you have a cat 1 then you will probibly not be able to turn the passive arming off..... this is what makes it thatcham approved...........
there would be no point in fitters fitting an alarm which you could turn the auto arming off as most people would turn it off and forget to arm it every time they leave the car...... petrol station forcourts come to mind! and the car would get nicked........ or at least something would get robbed!
once armed it shouldnt really go off unless your windows are down of which you should have a sensor disable button so when it self arms you press the sensor disable button (normaly there are 2 button on the remote this is normaly the 2nd one) and this will disable your ultrasonics so your alarm wont go off unless they open your door...... i have to do this myself!
another thing ive learned with mine is if i get out arm it and then disarm and open the door and then close the door this fools the alarm into thinking ive got in the car and if i dont put the key in the ignition it just arms the immobiliser not the alarm!

a few tips for you........