Minecraft wiki entry for Development_versions, associated text: Added functionality.
Has the ability to "shriek", emitting ring-like/sonic particles.
Is activated by a sculk sensor, redstone signal or player's stepping.
Sculk shriekers summon wardens only if there isn't one within 48 blocks.
Gives players the Darkness effect when activated.
If activated three times, a warden is summoned from the ground.
Player has 4 levels of warning_level (0-3), everytime activated, the levels increased by 1, and never decrease.
If a player had successfully summoned a warden, only one attempt is required to summon a warden next time.
Currently does not drop when broken, even when using silk touch.