Most underground power line detectors operate on the principle of electromagnetism. The system typically consists of two main parts: a transmitter and a receiver.

• Passive Locating: This method relies on the receiver unit to detect the naturally occurring electromagnetic fields radiating from an energized (live) power line. While this is a quick method, it may not provide high precision and only works for lines carrying a current.

• Active Locating: This is the most accurate and reliable method. A separate transmitter applies a specific, traceable electromagnetic signal onto the target line. The handheld receiver is then tuned to this exact frequency and can precisely trace the path and even estimate the depth of the buried cable.

Some advanced locators also use Ground-Penetrating Radar (GPR), which sends radio waves into the ground to create a subsurface image. While GPR is useful for locating non-metallic objects, electromagnetic locators remain the primary tool for finding power lines.