Security tip-detecting CCTV looping

In several movies we see con men breaching CCTV security system, by hacking into CCTV circuits and looping the video. This fools the control room folks monitoring CCTV footage into believing that everything is normal, while the con men begin their act breaching into the premises.

I don't know how this is actually done. In some movies, this is achieved by one of the guys cutting some wires, fixing an extra gadget... in some other movies, CCTV looping is achieved by attaching some sort of magnetic device/circuit to the CCTV itself. In some other cases, this is done by a set of computer commands.

I was thinking how to secure the building against such an attempt of sabotage? I came up with a simple idea.

In front of key cameras, fix an analogue clock. This clock would keep running and should show current time in the monitors showing CCTV footage. If the cameras are hacked and looped, footage would show an earlier time and will show same time again and again every few minutes. Security folks monitoring the footage must randomly cross check if the time shown in the clock is correct.

Image from auratech.pro and jonah33.com

If I was a highly paid security consultant I would have sold this idea for few million bucks to high profile clients. Since I;m not, just sharing the idea with public. Hope right people will spot this idea and put it to right use. Do comment