I have this alarm fitted in my GS (it was already fitted when I bought the bike). It comes with a four-button fob. The buttons are 'A' (arm), 'D' (disarm), '#' and '*'.
There is no way to arm/disarm the alarm from the bike itself. When I just got the bike, the alarm would automatically arm about 30 seconds after I shut off the engine. The only way to disarm it would be to press the 'D' button on the fob.
If you don't turn the ignition on within the 30 seconds, the alarm would arm again. This was extremely annoying, especially when doing any maintenance or anything else on the bike. It was also very-very overzealous and any slight movement of the bike, even just slapping the top-box lightly, would set it off.
This thing was annoying me like there's no tomorrow. Needless to say, there was no documentation of any sort coming with the alarm. When I asked the PO about it, he said that he bought the bike with the alarm already fitted and no documentation. I searched everywhere for the documentation for the alarm - and the only thing I could find was the site of the manufacturer, who wanted about $10 for a PDF version of the fob manual and another $20 for the PDF version of the alarm manual. Download Manual Juego Caesar Iii on this page. Yikes! Once I was annoyed enough enough and started just randomly pushing the buttons on the fob. I don't know what I did, but some settings changed - and now the alarm would only come on after I turn off the ignition. If I disarm it, it would not arm itself again unless I press the 'A' button.