Sorry for the delayed response but I just bought one of these and am just joined the forum.
The Parking Mode requires that the unit be powered ON for P mode to work. The P mode could also be named "THE MODE THAT THE DEVICE GOES INTO AFTER THERE HAS NOT BEEN A CHANGE IN THE DIGITAL IMAGE AND THERE HAS NOT BEEN AN IMPACT FOR 5 or 10 MINUTES (as User selected)" but that is too long a name :>)
Essentially the P mode just saves memory space. By the way, the device triggers off motion from the rear camera AND the front camera. For long term vehicle storage, be aware of potential battery drain.