That is to say they allow you to look back at an event but unless you happened to be viewing the monitor at the time they don’t allow you to react to an event.
However adding remote-monitoring facilities to a system can change it from a passive to an active security solution. Transmission facilities can be added to any CCTV system giving the opportunity to view the images from a remote location. Just remote viewing however does not make a system active indeed the same conditions apply if you are not viewing at the time of an event there is nothing you can do to react to it.
The choices to convert remote viewing to remote monitoring are either use the services of an alarm-receiving centre (ARC) or employ detector-activated transmission to alert you to view your images remotely. Using an ARC involves ongoing monitoring costs but does have the advantage of dedicated staff available twenty-four hours a day to respond to your CCTV.
Movement detectors and or video-motion-detection can be used to trigger an alert when unauthorised movement on your grounds are detected. Viewing your system over the internet or via a smartphone you can then react to events as they unfurl. If the local kids have jumped the fence to retrieve a football you can rest easy but if intruders have been detected you can take positive action.
If you require an automated and guaranteed police-response however then the system would have to comply to BS8418 (see police-response CCTV page).
The type of remote viewing and monitoring can be quite bespoke and need not necessarily involve ongoing monitoring costs if you in effect are doing the monitoring.