What is Motion Detection and Why is it an Important DVR Feature?

Motion detection is a DVR feature whereby live scene data from a camera is constantly analyzed for activity which might be deemed to be a moving object. Once enough activity is detected, an event is generated and recording starts along with perhaps more actions.  From a functional standpoint, most DVRs handle motion detection events almost exactly the same way as alarm events tripped by an external sensor connected to an alarm input.  The main difference is that one is labeled "alarm event" and the other "motion event". The following are the basic configuration attributes that most DVRs use to define how motion detection operates:

	Schedule  If not full time, the schedule for when motion detection is enabled.
	Mask Definition  Lets you remove (mask out) sections from scene examination.
	Sensitivity  Define parameters used to differentiate real movement from scene noise.
	Pre-alarm Recording  Amount of buffered video that occurred prior to motion detection to be inserted at the beginning of the recorded sequence.
	Post-alarm Recording  The minimum length of recorded video from the point activity was detected. Longer sequences may be recorded with continuous scene activity.
	Miscelleanous  Depends on specific DVR model, but examples would be activating alarm outputs, sending email alerts, uploading still images via FTP to a web server, etc.

Motion detection is important for two related reasons.  First, the amount of hard disk space used to record video for a 24 hour period is dramatically reduced.  This is because all dead time where nothing happens or changes in a scene is eliminated.  Despite the possibility of "false alarms" like a nocturnal bug flying by or even moving tree shadows, the storage savings is huge.  The resulting second benefit is that searching through archived video is quicker and less painful in that you're now only observing action shots.

One last crucial note about motion detection.  It is vital that the DVR have the above mentioned Pre-alarm Recording feature with a generous buffer.  Because sensitivity often has to be adjusted down to prevent too many false motion alarms, it is often the case that events of interest aren't triggered until the subject or vehicle comes into full view.  Therefore, it is very useful to see what happened anywhere from 5 to 20 seconds prior to activity detection.

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