Munter hitch
With your rappel line set up, grap the line with your thumb down as shown
Bringing your thumb toward you and flipping your hand over will give you a loop like this one.
Now without letting go of the loop, grab the rappel line above the loop
Clip your carabiner around the two sections you are holding by clipping from the back of your hand to the front
Grab the carabiner and pull down to pop the hitch through the carabiner
And you're ready to clip in and go
A quick and neat rappell/belay device that provides lots of friction. Excellent backup,
does put alot of twist in the rope though.