Question about distance measurement on motorway

Hello, was yesterday over large distances on highways. In places were attached to bridges distance meters, which could be seen accordingly. Now my questions: 1.) If you are recorded by such distance measurement, do you notice this at all or do I only know this afterwards, if I possibly get a fine notice because of too little distance? 2.) Do these devices turn a video of one in the course of the distance measurement? Finally, it must be checked if necessary, 3.) If a video is shot – can you clearly recognize the driver of the filmed vehicle? Question because I am not sure that I have always kept the prescribed distance at higher speeds. Of course, I am now concerned that I was filtered/recorded unnoticed by a distance meter and then received unpleasant mail in a few weeks. H open times that there is nothing coming… Thank you for the help, otter