A metal detector can be used to find metal materials buried underground or hidden somewhere. A detector can be used for finding lost valuables on the beach, and they can be used at security checkpoints to locate weapons. You can build your own metal detector, using a few household items.
Attach a piece of Velcro to the back of the AM radio using the self-adhesive backing. If it doesn't have any adhesive backing, then use a bit of glue. Do the same with the calculator.
Attach two pieces of looped Velcro to the interior of the CD case. There should be one piece for each side.
Mount the AM radio and the calculator to the interior part of the CD case using the Velcro strips.
Turn the power on the two electronic devices and then tune the AM radio to the highest frequency where you can only hear a static sound.
Fold the CD case together. When the calculator is near the AM radio, the radio will emit a loud distinctive tone. When you move them apart from one another the sound will cease.
Test whether the metal detector works by placing the CD case near a piece of iron or any other piece of metal. You will hear the loud tone that you heard earlier when you placed the two devices together. Test this out with different types and sizes of metal and you will be able to hear a slightly different sound for each. This can be useful for identifying the type of object that you found.