My car DVR setup & results
 

I started with a $91 unit from Geekbuying.com that clips to your rear view mirror, because California law doesn't allow window -mounted devices outside of the lower left corner of your window. Mirrors are exempted. This is what my unit looked like.
http://i1179.photobucket.com/albums/...psa090cc97.jpg

I wanted a unit that has an auxiliary camera mounted on the rear window, and this unit has that. Most units with rear cameras take photos of the occupants.

The geekbuying unit had some issues. The auxiliary camera's lens quality dropped off a cliff one day, like the lens elements delaminated. And the audio recording quality was always poor - like a blatty loud-exhaust Civic riding inside the cab.

So I replaced my mirror-mounted unit with a $55 eBay car DVR that mounts in front of the mirror, where it doesn't block my forward view at all.
http://i1179.photobucket.com/albums/...psddca42ca.jpg

http://i1179.photobucket.com/albums/...ps7f309809.jpg

Here's what it looks like with the mirror tilted out of the way.
http://i1179.photobucket.com/albums/...ps99499338.jpg

And here's a view of the auxiliary camera (the cylindrical device under the third brake light).
http://i1179.photobucket.com/albums/...ps06c2d3bf.jpg

You can see some of the results in my Hall of Shame videos. f you want to read the circumstances with each video, click on the link at the top of the video.

http://www.youtube.com/watch?v=7ZZNliX9oUI

http://www.youtube.com/watch?v=8I9EwxUqQnQ

http://www.youtube.com/watch?v=d7H4Uz1951Y

http://www.youtube.com/watch?v=FgE0yGg_00I

http://www.youtube.com/watch?v=W37z9WuUmE8

http://www.youtube.com/watch?v=fb-t5CLm9nE

Why you should get a car DVR.

http://www.youtube.com/watch?feature...ouCS4Weag&NR=1

The unit I bought on eBay

can you trim the videos down to the interesting parts?

looking at some other vids, it seems like half the time they are self incriminating. I could see them being confiscated at the slightest infraction for review. P&G could get you 10 speeding tickets if they review the tape?

It seems the red light cameras around here are disappearing, which is good IMHO.

Not sure what is worse, snotty kids or angry cops. I'm reasonably sure the video would not garner as much "support" if they included what preceded the officer getting angry.

Thanks for the tip/incentive to trim the videos. I used YouTube's handy editor and trimmed them to essentials.

My videos are my property. I can envision situations where they might be subpoenaed, but none where they could be legally confiscated.

I also don't see me ever getting a speeding ticket for P&G. The PSL is my uppermost speed, and I've never gotten a speeding ticket in >50 years of driving.

Thanks for editing. I actually grabbed one off ebay cuz it was less than $60 and I can use it as a backup camera as well so thanks for the link also.

How many minutes does it go back?

Thing is if they pull you over for something then it can become evidence. Also, I don't pay perfect attention to PSL or my dashboard, I focus on the road.

note: I may pull out the built in camera and wire in an extension cable so I can put the display anywhere (can't see it behind the mirror)

I can imagine it now: little yellow/black decal (like old "Baby on Board") that says: "Event Video Recording In Process" ... for law enforcement "moderation" purposes!

Then they'd try to pull you over for "harrassing" a police officer... or some such nonsense. Citizens recording police is growing to become a big issue.

I might just go out and buy one of these DVRs, now.

Citizens have every right to film police on public roads and in public places.

P-hack, it depends on the DVR, but the three models of car DVRs I've owned take ~50 MB to record 2 minutes of HD MP4 video, or ~70 MB to record 2 minutes of HD MOV video. They simultaneously record an auxiliary camera VGA file of about half that size. So, at 75 MB for 2 minutes of MP4 video, or 100 MB for 2 minutes of MOV video, a 32 GB SD card will let you go back through 10-14 hours of video before it loops to overwrite older files.

Please note, some states are two party consent states- EVERYONE being recorded must AGREE(or at least be aware) that they are being recorded. There are quite a few horror stories in Maryland like this, from people trying to tape the Police on the road to phone recordings attempted to be used in court.

That sign thing is a good idea. In Ohio, I know it is fine-but I would explore your laws in your state.