As
jokiin mentions the way motion detection works at least on the 027 was it would start to record a few seconds after it noticed motion in front of the camera. So if for instance someone bumped your car or took your mirror off The camera would record a second or two after it seen the car pass.
I tested it out in an empty car park a few times. i would be parked up in a straight facing space where cars are driving down passing on my cars left. There were no other cars or motion around other then one passing ever 5-10 mins if that. by the time the camera started to record anything the car would be about half a car length away to far for a plate, but you could probably go Okay that was a blue Nissan Pathfinder that bumped my car.
I started out the same way. grabbed a DVR-027 because i was new to everything and wanted to have at least something to protect myself from bad drivers, but did not want to invest 200+ dollars into something that may have been misrepresented or missing features i needed. Once you read up understand everything things are not to bad. If i knew then what i know now i would of defiantly grabbed a higher end camera sooner. I love my Vico, but i can understand how hectic it can be at first.