Hi CarlC,
I realise that you are asking about systems that do this - with the continual incursion of smart electronics into our daily lives I thought I would suggest a possible route around that.
The programming to connect smart appliances is based on IFTTT for better integration of disparate smart objects such as TV's and network cameras, it's the old programming classic - IF 'this' (Camera PIR sensor triggers ) 'then' 'that' - if this then that -
thinking in terms of electronics it's like 'logic gates' in schematics -
If you have any android devices you could look into IFTTT for google, I think you might need a Chromecast to turn any TV into a device that will take commands from 'Hey Google' - with IFTTT you could set up a chain of events such as Notification received from Camera 1 - Hey Google play Camera 1' - You don't have to do any talking to the devices you just set up scripts and routines to run when the first notification happens.
Hikvision has an Alexa skill so in theory you could put a 'Amazon Fire Stick' in the TV and set up some kind of routine with the Alexa skill to play whichever camera you have been notified about automatically overiding whatever was previously playing or turning the TV on into the App and displaying the Cameras.
Also there is the possibility of using a third box such as an android box, Rasperry PI to set up some kind of Ad Hoc network around your current setup and crucially to stream the motion triggered camera through your display.
The above is of course all built on integrating your current DVR/NVR or Cameras with your TV setup.
As for the Scart Connection thing, I'm thinking that was possibly irrelevant and it was more of a priority thing: your DVR would have possibly been in a passive state and woken up by the notification this would have taken priority over sources and automatically changed the source on the TV from AV to Scart for example - TV's have loads more inputs these days and there is often a menu tucked away where you can set priorities, though inputs often work on a rolling basis so if I turn on my xbox it will switch to that hdmi, but if I then ask Alexa to play the Camera app it will switch to the firestick on USB; I then ask Google Home Mini to play a video on youtube and the TV springs to another HDMI port with the chromecast, I play a video from from my iphone and it is cast directly to the TV via 'Wireless Display' -
You ask a very interesting question and I am thinking about other solutions - it could be something to do with the Television you had at the time as well; I had a fancy TV once that had PIP Picture in Picture built in so that a small screen would pop up when there was an instant message on xbox live but can't remember how we set that one up.
On balance I'm also thinking that your DVR would have possibly had an option somewhere to 'broadcast' a camera to your display output when motion detection had been triggered, that would be a logical explanation and since you had a scart lead this took priority over whatever else was displaying on the the TV. - I guess a lot of great features get left out sometimes when they are adding all of the new functionality to tech - I am sure there will be a way to do this though be it hardware/software or a mixture of the two.
