Alarm trigger code 20 & trailer

After having a couple of early hours of the morning alarms I decided to hook the car upto vcds to find the trigger. 

The last trigger was 7 (trailer) - Any ideas why the trailer should be triggered? I have a towbar but the trailer wasn't on at the time.

The previous trigger code was 20? Its not listed on my list of codes - any ideas?

Doesn't seem to have happened since I put the battery on charge overnight just in case it was a low voltage.

cheers

steve