I have a Swann 4-Channel, 2 Camera DVR System and the way this works is as follows: The DVR continuously records from all cameras. There is very advanced motion detection. Its default settings are great but you can also specify certain areas for motion detection too. Once motion is detected, that portion of footage is bookmarked for playback later as an "Event". Each time an "Event" is created, I believe, but am not 100% positive, you can set up the system to send a notification via the mobile app. I am going to attempt to do this soon, I just acquired my Swann system yesterday and am still going through all of the set-up.
I hope this helps.