Mine used to randomly goes off, sometimes consistently for a while. The common conclusion is that the alarm siren unit has a dead or dying battery (if you search for siren/alarm here). Which is also common on A3/TT sharing the same unit. I also have VAG-COM, which when my alarm went off at random, I ran diagnostics and the glass breakage sensor had repeatedly came up.
However, I've never gotten round to replacing mine and have not noticed the alarm goes off randomly after I replaced my car battery in December. That leads me to think a dodgy car battery made also trigger the sensors and trip the alarm.
You should get someone with VAG-COM or a friendly garage to first clear all your fault codes. Then when the alarm goes off, take it back for a diagnostic and see what's tripping the alarm, the ECU has a record which sensor caused it. Then work from there.