I made a house with a floor level that had an air block between it and the ground, but I wanted to make a cool basement trapdoor, so I came up with this. It's pretty resource intensive, but I tried to go for compactness. I'm pretty sure there's still some blocks to shave off, but this is the best I can do with my current knowledge of triple piston extenders.

• Made in 1.13.2
• Note blocks used as updating blocks can be replaced by pistons
• Optional tripwire closing circuit