I have been leaving at least one of my cams running in the truck, while parked overnight, with the hope of detecting vandals, thieves, and other vehicles that may hit my parked truck while I'm away from it, or sleeping.
In normal operation, a dash cam will continuously record, save segments, and erase the oldest segment on the card by recording a new segment over it. This is called 'looping'.
How much coverage you will get on your card depends on the card memory size, and the resolution of your camera. Most of the 1080p cams will maintain the last 4 hours of video on a 32gb card.
This isn't so bad, if you are sleeping in your truck, and somebody breaking into your truck, or another vehicle backs into you truck and flees before you can really wake up and see much.
You can then review the most recent files on your card and possibly see what or who it was.
If you have left your truck parked somewhere, unattended, for an extended period of time, with your cam running in normal mode, it's possible the segment containing the information you want, may have been erased.
I see 'motion detection' mode as a strong possibility to give you some extended parking protection, without dealing with elaborate camera or memory systems.
No, you won't catch everything!
One dash cam will only provide coverage in one direction. If you have it mounted in your windshield, somebody walking up from behind your truck and trying to break in won't start the camera. Likewise, a vehicle striking you from behind isn't likely to result in much useful video in a forward facing cam.
The goal is to add a little more protection, using a dash cam you have to protect you while driving.
A further limitation on motion detection mode usage in long term parking situations include the battery capacity of the vehicle you have the camera in.
If you are reading this, thinking it will work in the car you park for days at a time, you are out of luck. While your typical dash cam only draws about .35 amps, it's enough to kill some car batteries after a few days.
(this is not a problem usually in large trucks, which often have 4-8 batteries.)
Few cameras also have a 'pre buffer' capability, meaning they always record, and save a few second of video BEFORE the motion detector sensor is triggered.
Don't expect miracles, but you may be surprised at how often video from this mode is useful.
Let's look at some video clips for motion detection triggered samples from some currently available dash cams.
Here's a Mobius Wide Angle cam on a brightly lit day.
(All segments start when the cam was triggered, but are not shown in full length)
The next two from a Papago! GoSafe 110, parked in two, different truck stops, with probably better than average lighting.
And the Mobius Wide Angle, again.
