Intrusion detection
Intrusion detection, in video security, is a detection that raises an alert when a person or vehicle enters an area or crosses a boundary where it should not be. It comes in two forms: line intrusion, a virtual tripwire across a boundary, and zone intrusion, a polygon over an area that should stay empty.
A line rule fires when a confirmed track crosses the line, optionally in one direction only, which suits fences, gates and thresholds. A zone rule fires on presence anywhere inside the polygon, whichever way the subject came in, which suits rooms, cages, yards and rooftops.
Both depend on the quality of the tracking underneath. A detection that fires on a confirmed object track ignores shadows, rain and headlights; one that fires on pixel change does not, and becomes a false alarm generator at night.
On Camzify line and zone intrusion are licensed as an instance per camera, each with a notification window, so a zone over a stockroom can be silent in working hours and live after close. Both feed the patrol round as a check at that camera.