You can use this A88 Metal detector non-contact metal induction detection module as a metal detector. When it approaches any metal, it makes a sound.
This is a module specifically designed to detect metal. The module operates by inducing currents in metal objects and responding when it occurs. A nice onboard buzzer signals when it detects something and an onboard potentiometer allow adjustment of sensitivity.
The power cables of the Metal detector non-contact metal induction detection module will need soldering on for the module to function, positive to the outside of the module and negative between the potentiometer and an electrolytic capacitor.
 
Features :
V+ Connect to power positive
V- connect to power negative
Adjust the potentiometer, let the modules work normally.
Small and easy to use module.
It comes with a Buzzer for metal detection indication.