Locking volume at safe maximum?

(I tried the New Ideas forum for this but they locked me out...they obviously know something.)  But this is the great all-purpose forum so I'll post it here.

New concept or old idea, I really don't know.  It is this:  We know that when the system is installed we find the maximum point on the head unit volume at which there is clean signal and no distortion.  Then we adjust the amp gain to that signal.  If someone were to mess with our stuff without us being there to supervise, they can easily turn that volume up past that point and possibly do some damage.  I haven't heard of any locking devices that can be installed on a HU to limit the volume to that particular max point.

I can think of three ways.  One is simple and not at all foolproof.  It is what I am going to do.  Place a red arrow sticker on the HU at that critical point.  I'm using a HU that has dots going left to right.  It wouldn't work with numeral readouts.

Better, a volume knob that has a pointer sticking out, and an adjustable.knob just behind the volume.  You set the adjuster, and the volume knob can only be turned up to the point where the pointer hits the stop.  This works only on normal round knobs.  I've seen this on something else before but I can't remember what.

Then for all those push button type radios, there could be something that the manufacturer would have to add.  A 'max volume set position', so when you find that point you can push the 'max' button and the volume will never go past that point.  Maybe even get a Robbie the Robot voice "DANGER! Will Robinson!"  Maybe also send some voltage to a hidden Bass Shaker in the driver's seat

Are there units available with a feature like this?

Oh, ya know I didn't even think if it that way.  In my mind it was we, meaning all of us who get our system tweaked right but have wives and girlfiends and teenage kids and their friends...etc., who have access to our cars.  It's the head unit volume that they will crank up.  For example, my HU delivers clean signal to exactly the halfway point, and anything above that is distorted.  I know the limit, but there is now way to stop it from being turned higher.  And I figure that's just as bad as tampering with an amp.

Actually there are several power limiting devices available in the professional audio world that are used to protect speakers and amplifiers from being over-driven.  HERE'S a page from Rane that describes one of their products.  The same ideas and circuits could be applied to car audio... indeed, it sounds like a potential money-making product if done right...

Sorry dude, I too interpreted it as a customer issue, not a personal one.  Nods head