Kekkai can be configured so that a Kekkaishi can sense when a being possessing an evil aura breaches them (such as the Kekkai around Karasumori Academy). This makes them ideal tools for protecting large areas or buildings, so long as the Kekkaishi has enough power to completely surround them. Likewise, Kekkai can also be used to pinpoint the locations of enemies already present in an area.