Timber or metal studs?

[Stephanie]

I want to install a floating shelf, but I'm not sure if I have metal or timber studs - is there an easy way to find out before I start drilling into the walls?

[Kermit]

A stud finder will tell you if it detects metal. 

[Stephanie]

Oh really? I thought they just detected where the studs are. 

Thanks for your help.