Empty air sandwich
Terrarian
Exactly the same as the player-above sensor but for enemies. Preferrably non-critter enemies. Would help for new base defenses.
- Traps on ceilings and floors and walls that automatically trigger as enemies pass the area, possibly inside arenas too
- Automated traps mounted on the outside side of a building and prepped to scan for flying enemies that keep bumping onto it like they always do
- Automated monster pitfall traps that open and close on their own, because you've always wanted one
- A monster sensor placed with some wire that connects only to the two sides of a door and not the center, so all it does is auto-close doors if they were open when a monster comes nearby
- An actuated block wall that naturally stays open and only closes when monsters are around