On one coil, attach an earphone. Carefully wrap each wire end onto the earphone jack so that the two wires do not touch each other. Secure with tape.  (See diagram below)

Close up of connection:
Step 4. On the other coil, Connect it to a battery and a motor in series (making a loop).  You can add a switch in the circuit loop if you desire. See below:
Now you have the ingredients for a metal detector!