Carpet trap

Instructions:

1. Place an empty chest somewhere (preferably outside your house) 

2. Place carpet around the chest. 

3. Make a hole below the carpets. Make sure it is at least 2 blocks deep (the deeper, the better!).

4. (Optional but highly recommended) Fill the holes with spikes or lava. 

5. (Optional but highly recommended) Place a sign next to or on top of the chest. Write "Free diamonds" or "Illegal items" or something like that. 

When someone steps on the carpet, they will fall into the hole and get trapped/die.