Use radio waves to find metal objects buried in the ground!

You will need:

CD case
Small radio
Calculator
Sticky tape (preferably double sided) 

Carefully remove the part of the cover that holds the CD.  This should pop out, but you may need help from an adult.

Stick the radio to one side of the CD case, facing in.

Stick the calculator to the other side of the CD case, facing the radio.  As with all electrical equipment, the calculator emits a weak radio signal.

Turn on the radio and tune it into the top of the AM frequency.  Turn up the volume and close the CD case until you hear a clear, loud tone.

Now open the case until you can only just hear the tone and go and find some metal!

When your metal detector detects some metal, the tone will get louder!