Inductive proximity switch?

[psr17]

Hi all
First time here but been lurking a while, I think what I'm after is a inductive proximity switch, basically what I'm after is a switch that is triggered when a ferrous metal is close by

I'm trying to make a detector to identify nails in timber, I know one can be bought but where's the fun in that, looking to use a 9v power supply

Any advice or guidance is appreciated

 

[Minder]

What diameter or area do you need to cover?
For the most part it is not worth building one.
M.

 

[psr17]

I was looking at a 25mm radius, I know I could buy one but where's the fun in that