Sculk veins should work as connections to sculk sensor/shriekers.

As the sculk veins are already named that, they clearly are supposed to be part of the group of living organisms that is sculk. As it has fungi-like attributes, it should be able to sense contact/vibration in one part of it's network and relay that information (maybe through a sort of charge like in a system of nerves) to the nearest "decision-center" like a sensor or a shrieker, if it is connected to it. A similar technique to how sculk spreads with the xp charges could be used, moving only through sculk veins but being able to activate sensors and shriekers if close to them (sensor) or directly connected (shrieker). Such a charge could start small if you just touch one vein briefly, but if you walk on them (crouched or not) the charges get bigger and can activate sensors from further away as the charge itself start making ever stronger vibrations. If the network of connected veins is no longer touched, the charge diminishes relatively quickly. If a vein is brocken, a minimal charge starts on the neighboring veins. A charge should always travel through the entire connected network before diminishing at an end point. 

That would also make sneaking through the city much more challenging.