Scale only part of a block, keep the other part a constant size

[mickeforsberg 10]

Hello!

I'm looking for a solution to my problem. I have a block (center in the attached image) that I'd like to be able to scale as usual, but I want the red circle to remain the same size always. This particular one is a symbol for a smoke detector and the red circle is supposed to be the coverage of this detector. That is why I want the coverage circle to remain a constant diameter of let's say 10 meters, but I'd still like to be able to scale the smoke detector symbol depending on viewport scale. I also want the circle to follow the detector so that I don't have to select both.

Other requests are the ability to freeze or turn off visibility of the circle, but I'd still want it to follow the smoke detector if moved.

 

Is any of this doable?
What are your thoughts? Thanks! 

Edited March 23 by mickeforsberg

[BIGAL 298]

Dynamic block so circle is always a fixed rad.