Monster Manual, page 138
False Appearance. While the shrieker remains motionless, it is indistinguishable from an ordinary fungus.
Shriek. When bright light or a creature is within 30 feet of the shrieker, it emits a shriek audible within 300 feet of it. The shrieker continues to shriek until the disturbance moves out of range and for 1d4 of the shrieker's turns afterward.
Underdark