Or if you've got auto-dimming mirror, just run it off of that harness.
As
@ralphc mentioned, you can get the kind that fit over your mirror or better yet, one of these units that replaces the OEM mirror:
The only problem with these is that they tend to be jittery when you've got your bass popping.
There are also "stealth" units that fit onto the plastic shell of the LDWS cover if you can find one that is compatible with your car. This one here is for the Cadillac ATS:
Ends up looking like this installed:
(IDK why this guy has two dashcams installed.)
If you live in a hot environment, they you want to get one with supercapacitor instead of a battery.
In general, the Korean ones are the highest quality with the most features but you're usually paying somewhere between $100-200. The Chinese ones, you're paying $30-50 on Amazon but you're also getting Chinese quality.