First of all, I know this is an old post sorry, but...
I have very simliar symtoms on an oiginal Honda alarm....cars is a 98 1.8Vtec
My alarm goes itself after about 1minute of arming it, I stood next to it yesterday and waited, and sure as hell, after a 1minute or so, it went off.
I read that a dying battery can possibly cause it (cars own I take it) as mine's fine..
Where's this shock sensor...and could that cause it, although no one's touching it, I'm just standing next to it waiting.