Metal Detectors/Magnetic locators find objects with ferrous or iron content. They do not react to other metals such as copper, brass, or aluminum, as metal detectors do. Therefore they are less subject to interference from surface debris. Magnetic locators work deeper, measuring a magnetic field originating from the buried target, whereas a metal detector can only detect shallow objects, typically 9 to 12″ inches maximum. Other names include , Valve Box Locators, Manhole Locators & Curb Stop Locators.