Minecraft wiki entry for Sculk_Sensor, associated text: Wool has a special interaction with sculk sensors. If a wool block is between a sensor and a vibration source, then that sensor is not able to detect the vibration. Sculk sensors are not able to detect footsteps on wool blocks, nor can they detect when wool block items are dropped. Vibrations are produced when wool is placed on sculk, but no vibrations are produced when wool is placed on top on any other block.‌[Java Edition only]