I guess it depends on how the sensitivity is set, but it wasn't uncommon for smaller metal items to set ours off.
Ironically, our knife sharpening service (yes, all kinds of ways to become a bidness man in the US) went right through security with his open box of knives till passengers complained. (LOL!)
After that he had to drive out to the concourse with an escort.
Correct me if I'm wrong, but weren't small (<3" blade) knives legal on planes up until 9/11?