If you are trying to make a sculk sensor, you are probably playing around with Redstone. However, you cannot make sculk sensors in the game as they are a block only found within the new deep dark cave biome that spawns after Y-level 0, deep underground.
This is also the same biome the warden roams around, but this won't be a problem if you are quiet. That said, you can find the sensor growing naturally deep in the biome, as shown by the image above. If you manage to locate one of these sensors, you will need to place wool blocks all around it before trying to break it.
This is because if you do it without woold, you will alert the creepy thing called the warden with a signal to the warden and attract it - you do not want this, as the warden is practically unkillable.
Related: How to kill the Warden in Minecraft
Because of this, we highly recommend bringing around eight to ten wool blocks to completely cover all sides of the sculk sensor to prevent an unhappy visitor from ruining your fun.
When you have done this, you will be safe to mine the sensor, and once you have it, you will be able to use it in Redstone creations.