It's pretty improbable that someone's going to take a critical part through the checkpoint concealed in their collar or hair, either, but I've seen a reliable TSO defend the collar searches here.

So the same people who can't find multiple pounds of ex**osive during a bag check at Fayetteville can be relied on to find something small enough to be hidden in a t-shirt neckline?

(I wonder if they scrutinize hearing aids).