dash cams are normally set on a loop which you have options on to decide, like 2 mins, 10mins, 20mins etc. If you want to capture something thats just happened like you've just dabbled with a GTR then you can press the OK button and it saves that latest loop and then starts a new loop. However, they do have a g-sensor, so in the event of a crash, the camera senses the knock and keeps the latest loop of recording. The one shown here from Amazon does this. You can adjust the sensitivity of the g-sensor. They are soley dependant though on plugging them ito your 12v socket as the batteries dont last long. So what if you want to keep recording after you've left the car, well you tap into a permenent live and a get a gizmo that will knock the power off if your car battery gets below a certain level. Not sure what the gizmo's called, but you can get them on ebay. Hope this helps.