Ok, i'm probabaly really really dense.

But about 6 times in the last month, i have jumped into my car as per normal, after unlocking it....and just before i start it - the alarm goes off....i have no idea what is causing it because i do nothing different - i noticed my foot was on the brake pedal wen it went off tonight....but it doesnt go away till i start the car.

Most likely your alarm wiring in one of the doors has disconnected somehow. My alarm would trigger when entering through the passenger side because my drivers side alarm connection wasn't even connected.
Might be something else, but won't hurt to have a peek!

might wana try to reset it if you have a reset option that is , my alarm use to do this in my bmw after i reset it it never happened again

is it the factory alarm?
also what model car is it (verada ei xi etc)