If you unlock it and do not open any door it will lock back in 60 seconds.
Ok, so when I opened the drivers door to exit and then the trunk it must have disabeled that feature. Any way to customize it? Locking after 60 seconds as long as the key is out of range would be ideal.
My '09 A4 would lock after 20 seconds or so when you walked away but apparently the feature was discontinued by Audi at some point. As mentioned previously, the doors will only auto-lock if the door was unlocked and no door was opened.