With accident recorders or mobile DVRS to give them their full name there are 2 types. Those that work and those that do not. You can pop into most supermarkets or big stores and buy a recorder that fits to the window for as little as £20. Quite a number of these give very good recordings both day and night. The problem with them comes with reliability. An SD card was never designed to be constantly written to and have a habit of filling up with junk files or even fail altogether. In testing we found that they could stop recording anf needed the card re-formating anywhere from a day to several weeks. To get a reliable recording you need a professional quality DVR. These will have smart SD card monitoring that will automatically format the card to remove the junk files. On our test vehicles we have had this style of recorder operating for over a year without the need to format or replace the card. They offer a fit and forget solution with an indicator LED to show the recorder is operating correctly.
We now stock a range of mobile DVRs that can record up to 8 cameras. These use AHD cameras to get the maximum resolution.