Metal Detector is an application which detects the presence of metal nearby by measuring the magnetic field value. This useful tool uses the magnetic sensor built-in your mobile device and shows magnetic field level in μT (microtesla). The magnetic field level (EMF) in nature is about 49 μT (micro tesla) or 490 mG (milli gauss); 1μT = 10mG. If any metal is near, the value of magnetic field will increase.
Metal Detector allows to identify any metal object in area, because all metals generate magnetic field which strength can be measured with this tool.
You might use the Metal Detector it to find electrical wires in walls (like a stud finder), iron pipes on the ground... or pretend it's a ghost detector and scare someone! The accuracy of tool depends entirely on the sensor in your mobile device. Please, note that due to electromagnetic waves, the magnetic sensor is affected by electronic equipment.
Metal detector cannot detect gold, silver and coins made by copper. But if it's a fake metal alloy in the gold & silver & coins, it will detect.