The Smart Lock series of Self Retracting Lifelines are designed to increase both productivity and safety on site. It better accommodates your natural work motions in both horizontal and vertical applications. Accidental and unintentional lock ups have been reduced by as much as 29%. The magnetic retraction system reduces accidental lock-ups and retracts at an evenly controlled pace. Unlike other SRL's with gear-based retraction, you can let go of the lifeline while it is fully retracted. Now that's SMART!