Is the claim that the speaker was at his wrist? If so did Biden have that hand close to his ear frequently?

I would think in general putting a speaker near one's hands would be quite risky given how likely someone would be to have their hand near the microphone and the risk of the mic picking up sound from the speaker.

I think if I were going to do this I'd use something like a bone/tooth conducting speaker. Much easier to hide and no risk of the mic picking up stray audio.