Along with Video Door Entry Cameras, NuTone had the VC1000 Surveillance Camera to cover larger areas inside or outdoors.
All of the NuTone Video equipment was considered very advance for its time. One of the more advanced design features was that both the Video Signal and the Power to run the Camera were carried in the same, single coax cable.
This was quite advanced at the time, unfortunately it was a techonlogy that didn't last.
The end result is that all of these systems are very difficult to replace and they will need to be rewired.