Slide the end loop of your safety harness belt over the handle end of the Halligan tool.
Face the window. Press the handle end of the Halligan tool firmly to the drywall 6 inches to the side of the window trim and 12 inches above the window sill. Poke a hole in the drywall.
Bring the tool upward firmly so that the length of the tool breaks the drywall above the penetration point. Slide the handle down into the wall cavity so that the axe head is lodged in the entry point.