That's how they work, they are always recording when your engine is running. If their built-in movement sensor detects a sudden jolt (hard braking, hard turn, a bump, a crash, etc.) it records a video clip - usually starting 15 to 30 seconds before the event takes place and the 15 to 30 seconds that follow - under a separate folder of the microSD card. That's called "Event recording". The rest of the times when you are driving and nothing happens, the recorder just stores 1 to 3 minute clips on a generic "Real-Time recording" folder that automatically gets overwritten by newer files as the card gets full. However with a 32 GB card installed, it's a lot of hours of real time HD recording you have access to. That's how I got the video clip of my bogus ticket to take to court, for example. There is also an option for "Manual recording" by hitting a button on the camera itself, if you see something really odd happening in front of you and would like to save it manually under a separate folder. I have a nice small library of traffic accidents that happened in front of my car recorded that way, lol... Here is one funny example of how SoCal drivers do under the rain:
http://www.youtube.com/watch?feature=player_detailpage&v=XSUoHhrYfmc
I actually will be wiring both cameras to my auxiliary battery when I install it, so that I may be able to enable "Park Mode recording" as well and have the cameras up and running even when I am not in the car. In that mode, the cameras stay awake even with the engine turned off, but don't save any clips on the microSD card unless they detect movement (such as someone backing into your car or approaching the vehicle on foot), then they save the clip (again starting 15 to 30 seconds before the event occurs) under yet a different "Park Mode recording" folder.
Clear as mud, right?

It's easier to understand once you see these little cameras in action. Too bad that the Vision Assist cameras on our cars don't allow recording of the video feed, there would be no need for all these extra cameras if they did.