Magnetic locators use existing magnetic fields to locate objects.
For this reason, magnetic locators will only detect iron and steel objects, unlike a metal detector which can sense all types of metal. The advantage is that a magnetic locator is more sensitive than a metal detector so it can detect deeper objects. Magnetic locators are commonly used by utility crews, surveyors, and construction workers to locate objects such as manhole covers, survey pins, valve boxes, and gas pipes. The sensor tube uses two sensor coil assemblies which detect magnetic lines of force. When no magnetic objects are nearby, the Earth's magnetic field is detected equally by both sensors and a low steady tone is emitted.