Microphone is in the trigger. You don't really *need* to push the trigger ever. It records video all the time there is power to the unit, and all the videos are saved until you run out of storage space, and only then does it start writing over the old ones. If you have a 128GB micro SD card, that would be a very long time.
If you short-press the trigger it saves a still image, plus a 15 sec video (10 sec of video before trigger press, 5 sec of video after trigger press). Nice because it easy to find what it was you thought was interesting at the end of the ride.
If you long-press the trigger, whatever loop is being recorded at that point is marked so that it is never deleted (for when you run out of disk space and it starts writing over itself).
But, if you have an incident/video you want to save, you will almost certainly download the video from the unit as soon as you stop (long before your unit would ever write over a video), which is easily done by connecting to the unit via wifi and copying the video to your phone.