Fotodiox Pro Pre-Trigger Remote Shutter Release Cable fits PocketWizard for Canon EOS 1D, 1DS Mark II, III, Mark III, IV, 1DC, 1DX, D30, D60, 10D, 20D, 20DA, 30D, 40D, 50D, 5D, 5D Mark II, III, 7D (replaces PocketWizard CM-N3-P), Pocket Wizard
This cable contains a Pre-Trigger Switch and a interchangeable Cable for specific camera.  When the focusing switch is on, the camera behaves as if the camera's shutter release button were held half-pressed continuously.  The camera responds more quickly and consistently in action, at the same time, it also consumes the camera's batteries much more quickly.  When the focusing switch is off, the camera will not auto focus, as if the camera set to manual focus mode, and the cable functions identically to the CM-N3.