I noticed today that the MMI Session ID List (SID) seems to correspond when the car is unlocked or, if already unlocked, woken up by opening a door etc...
For example, I've recently been away and my list indicates no activity for 15days.
I think the SID corresponds to when Terminal 75 becomes live.
The MMI Session ID list can be found in the Red Menu (Setup+Return) > Interfacebox > IRC > Available current Logfiles > Session ID List
Then use the rotary dial to go through the entries.
Previous to going away my car was with Audi for its MOT and this list showed me the dates / times they had the car awake.
It can't tell you if the car has been started but useful if you want to know if the car has been opened
