As I described there, the tune system has (perhaps inadvertently) removed the competitive distinction between televisions and security monitors, where monitors couldn't have their feeds shut off without access to the hub, allowing them to be used to detect intruders in particular setups.
Restoring this functionality while retaining the tune system is more complicated than it seems. I would propose the following solution:
Security monitors, by virtue of being in a security system, cannot be tuned without being 'unsecured' similar to a credchip/briefcase/e-note/etc. They have a four-digit (or whatever) passcode set, and when secured they cannot be tuned.