Under what circumstances, if any, can audio assistive technology be used in confession?

[This recent answer](/a/82538/53502) mentions that it is not permitted to use the internet or cellular communications (i.e., phone) in (private) confession. It also mentions a story of a certain catacomb with particular acoustics that allowed the priest and parishioner to be widely separated. Now, the answer (and in a sense, its related question) is dealing with desirable separation (e.g. for health reasons) between the priest and parishioner, which obviously raises a potential issue of them being able to hear each other. I understand why that digital networks are not allowed because they allow for the possibility that the audio might be intercepted, thus breaking the seal of secrecy that is supposed to exist. (Side question: are confessionals ever swept for bugs? 😉) However, this leaves me wondering, would a *closed circuit* system be acceptable? I'm thinking something like a microphone on each side connected to a speaker on the other. (Probably through an amp, but the amp would not be connected to anything else other than power. Thus, the chance of the audio being "intercepted" somehow not be appreciably increased. The simplest version of this, I suppose, would be some sort of closed-circuit telephone system such as what's seen on TV when someone is talking to an inmate.) p.s. [Peter Turner](/users/4/peter-turner) raises an interesting point, which is that one would think the answer to the above would be the same as whether or not a person using electronic [hearing aids](https://en.wikipedia.org/wiki/Hearing_aid) can partake in confession. I would rather expect there exists an official ruling on that, but I also wonder if that has been extended to other systems such as I discuss above and/or if there is a broader ruling on this general subject outlining what is and is not permissible.