Dash cams?

As someone else mentioned... make sure it has loop recording. I have a dash cam on my police car. It is constantly recording... but it only saves the last 30 seconds before you turn it on. That 30 seconds gives me plenty of time to hit the RECORD button and capture the previous 30 seconds and continue recording the present. That lets me capture information that I really wanted to capture without having hours and hours of nothing recorded in the off chance something happened that I wanted recorded.