From what I have read, the cam uses the battery of the car. So if the ignition is turned off, I don't think power goes to the cam, hence no recording is done. I am yet to get a dash cam, but I am seriously searching for. I have been reading many cam reviews on
this website, but can't pick one. Can I get a recommendation from a pro here?
You can wire the cam to an "always-on" circuit to ensure that it's always getting power, and thus, always recording. In my CX-9, I have my dashcams wired to the homelink rear view mirror. I used the Invisicord. Some dashcams have a parking mode that keeps it in a low power "standby" state until it detects motion. Others use a different parking mode where the camera records a time lapse until the motion detector is triggered, then it switches to normal recording. This is done to minimize the space taken up by the recording on the micro SD card.
Personally, I've been using the Viofo A129 Duo set of dashcams. The package includes a front camera and a rear camera, with WiFi capability, 1080p recording, parking mode, motion detection, GPS, etc. Been using this setup for nearly 2 years now, and it works great.
Also a note on the "always recording, constantly overwriting".. yes this is an issue, but if you buy a dashcam that can handle a large capacity micro SD card, and use a large capacity micro SD card, it doesn't really matter. Mine is always on and recording in 1080p, but I'm using a 256gb microSD card, so it will record 3-4 days worth of footage before it starts overwriting the older footage (and this includes the additional video files from the rear cam). If I come back to my car and see that it has been damaged, I can easily go through the footage.