Placing a tripwire hook updates blocks around an opposite facing tripwire hook on the same axis even when they are not connected.
See also Hermitcraft 4 Ep. 96- Wireless Redstone Door! (sorry cub).
- Build a setup as shown in the attached screenshot Tripwire hook setup (17w13a).png
- Place a tripwire hook on the gold block so that it faces the other tripwire hook
→ You will see that the trapdoor is updated and switches to the closed state