DriveCam is an interesting device designed for fleet operators or for families concerned with the driving habits of teenagers. It mounts on the rearview mirror and records the view out the front of the vehicle and also the view toward the interior of the vehicle. So in a split-screen playback you see the road in front and also what's happening inside.
The DriveCam records continuously, but the recording is automatically deleted unless something (like severe braking or swerving) triggers the device. In those cases, the recording from several seconds before the triggering event and the recording for several seconds after the event are saved for later viewing.
It's very Big Brotherish, but I can see how it could be helpful. DriveCam is pricey at $900 for the equipment, installation, and a one-year subscription. But it could prove to be invaluable in monitoring the driving of your children.