Please watch the video links provided, however to explain:
Video Analytics are generated from algorithms which convert real time video images into intelligent data. In simple terms, the data can be used to identify humans, cars, objects or people.

Alert Lines can be then set within the camera, these are generally known as: –

Line crossing – somebody or something crossing an analytic line in the camera (like your boundary wall/fence)

Intrusion zones – somebody or something entering an analytic area set up in the camera. – which may be set up just outside your property or within the street.

These analytic rules can be set up by day, time, size, etc to send alerts to the relevant parties, in the same way as your alarm alerts you/ your monitoring company, if someone enters your property.

In the case of the CCTV analytic alert, it sends a video clip of what triggered the alert, which the controller (in the case of Crime Watch monitoring the system) can determine if it is a threat and therefore dispatch Armed Response/ contact you, or something innocent.
This means that the controller or person monitoring the cameras does not need to look at them – the camera does the work for them. This is considered, in general terms, as being 95-97% more effective and accurate compared to a person monitoring the cameras. It is considerably more cost effective. This form of monitoring is often known as Black Screen Monitoring.