Core Principle Utility locators don't detect the pipes or cables themselves - they detect electromagnetic fields (signals) created by alternating current (AC) flowing through conductive (usually metallic) lines. A flowing electric current naturally generates a magnetic field around the conductor (perpendicular to the direction of current flow, following the right-hand rule from electromagnetism). The locator's receiver detects this field at the surface and helps pinpoint the line's location, depth, and direction.