Ear inspection will not catch a bone-conduction mike in a pocket or elsewhere on the body.
Hence, the need for jammer scanners against the signal. And Source of signal detection. Savvy tech people can do this, and probably will be doing this.
Hilary’s earpiece was plainly visible— white cream colored— annnnnd Donna Brazile fronted her the CNN answers, but the moderator got in zingers that pissed her off the edge of the stage and seat afterwards. Many quotes from the cameramen and other non-combatants.
Possibly I'm wrong, but I believe a bone-conduction mike only works if placed on the skull near the ear. If Joe used such a device it would need to be small enough to hide under his hair, which would be a challenge - LOL!
Just determine the signal frequency and overpower it with Kamala’s favorite rapper ... Notorious B.I.G. (see story about her today).