You can buy one already made down at the building supply place...wood handle @3' long with a round magnet the size of a hockey puck mounted on the end. Construction guys use them to pick up errant nails, thats what I used it for when I worked construction...Anyway, I've had one for years that lives out in the corner of the garage....It looks like a short little magnetty golf club....In our family, for some strange reason, we call this tool a 'Pud'.
I dont know why, its not the technical name of this tool, but everytime somebody loses something like a steel nut, bolt or screw out in the yard, or pins on the carpet, or the like, Ol' Pud is employed for that duty....Its funny!..the Wife drops a small metallic item, She is crawling around on her hands and knees in the living room or out in the yard, and then hollers, "I need Pud!"
Mud
I musta come up with the name for this tool sometime long ago...I think I told her 'PUD' stands for "Pick Up Device"
I bet if you ask for a 'Mag Wand Nail picker upper' down at the building supply place and they will know what you are talking about...dont ask for a Pud though, they may send you down to Bed Bath and Beyond ...