A self-blocking belay device allows a lead climber to give her second a belay while maintaining just a light hand on the brake strand. This is extremely useful when climbing long multipitch routes. The slack generated by the follower can be pulled in through the belay device but not pulled out; when weighted, the device and carabiner lock down on the rope. This allows the belayer to use her hands for other tasks (putting on another layer, getting food and water, or reorganizing gear for the next pitch) while still giving a secure belay. Note: manufacturers recommend that a light brake hand should be maintained even with a self-blocking device. Examples of such devices are the Trango B-52, Kong GiGi, New Alp Plaquette, and the Petzl Reverso.
As with belaying off the anchor with a Munter, the majority of your work escaping the belay is already done. By virtue of belaying with a self-blocking belay device your hands are already free and you have escaped the belay. The only step left to do is back up the system. Tie a mule-overhand or a backup knot onto the main line as a backup (fig. 3-14 shows a figure eight on a bight as the backup knot).