As a person who has designed, built and sold a lot of custom video interfaces out of my garage, I don't know if I agree with this.
I can say with a fair amount of certainty that most dash-cams are working at some voltage lower than 12volts internally.
Whether a vendor chooses to do that within...
For those that do not know this yet, the rear-view mirror compass receives 12-13 volts DC only when the car is powered up.
If you want to install a DashCam I suggest you use the hardwire DC-DC converter that SpyTec sells.
I think it costs less than $8
This converts 12-24 volts DC to a clean 5...