This very restrictive armbinder is a technique I learned from Sir C many years ago; my way of doing it has diverged slightly, but the main idea remains the same. Good for determined escape artists, but also potentially dangerous; tie with care and awareness of the risks. This armbinder can be made immobilizing even on someone whose elbows can pass each other, because the hands get pulled up the back at the end.

Note: in the video, I show using my normal quick shoulder harness; but you can actually get a slightly higher/tighter starting point if you don't join the top and bottom parts, and place the knot at the back of the neck.