I have a Blackvue 500GW:
http://www.amazon.com/BlackVue-Wi-Fi.../dp/B00B4E9764
This cam has a parking mode which idles when you car is off. (Goes sleep mode) and turns back on and record when they detect a shadow or movement. This is a feature that is included but can only be used if you hardwire it to your car.
TIP: If you have a dashcam only for the front of your car, when you park. Park backwards when available. No point in parking front inward when you get swipped from behind and dont see who hits you.
Furthermore, this dashcam is REALLY HD. I see everything crispy clear and you can also have live streaming as well as download your recordings.