A multiphase autocontainment field was an energy form utilized by Starfleet in the 24th century, designed to maintain a proper phase lock above three percent. In 2369, Montgomery Scott was surprised to learn of the advent of multiphase autocontainment fields, which were not used in his time, when a vessel's warp fields were designed to operate within a phase lock of under three percent. (TNG: "Relics" )