Security camera integration hack question

So my nvr does not have alarm outputs. I assume in POE cameras there is some type of voltage change over one of the pairs in the cat6 when it comes to triggering the nvr alarms from the motion and event activities that the camera picks up. Does anyone know if this is the case? Basically what I want to do is simply splice into whichever wire in the bundle is having this potential voltage event activity to feed over to a switch/relay that I can tie into my smarthome to carry out an activity.