Use Gold Detector App to detect any metal around you. In your garden or anywhere behind the wall. Use this app and it will start beeping once any metal comes into it's range. This app use the magnetic field of the smart phone to detect some thing with the help of radiation of mobile phone. Try to keep your phone nearby any metal and see if it is beeping. It will start beeping. If you have good smart phone, then you will be able to use this app very easily. It will give good results.