If you're interested, I have decided to bite the bullet and buy one of these 2ch motion detection recorders, and a couple of different cameras.
I'll report back on how good/bad it is. I suspect it's going to be very poor at night, when the car is broken into, but should be great for capturing accidents etc.
I have bought a CMOS camera, which is 2cm square, and a 1/4" CCD which looks small but doesn't specify dimensions, but which supposedly has better low light sensitivity (
Here's what I've bought:
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=330035611711
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=160035671245
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=250035852122