What do you reckon of these?

http://www.cnet.com.au/rear-view-mir...-339295948.htm


This device clamps onto your existing rear view mirror and is powered by the cigarette lighter, so installation is relatively simple. It features a 2.5-inch LCD on the left side and an adjustable lens to let you zero in and instantly play back what's being recorded in front of your car. You can set the video file size from 30 seconds up to 3 minutes, and it automatically begins recording once you start your vehicle and turns off once the engine stops.