BB
How do they know .... incursion sensors/Mk1 eyeball/Apolgies or Warning via R/T etc.....
Your idea of a mechanical device I believe has been thought of before .. problem is that everything mechanical fails at some point.
Not being able to enter a RWY would certainly reduce the risk of incursions
The method being tested has the advantage of using what's already in the a/c and requires only a relatively cheap change on the airfield
