Under what circumstances, if any, can audio assistive technology be used in confession?
Before answering this question further, I would like to mention an important point. Visual contact and/or a physical presence, even if behind a screen is absolutely necessary.
Generally speaking there are no sacraments that can be received over modern forms of communications, including over land line or cell phones, etcetera. You can not baptize someone over the phone.
Nevertheless some confessionals, I have been in, are equipped with a form of hearing aid strictly for use between the confessor and the penitent only. As such secrecy is maintained. Again, a physical presence equally been maintained.
Two way phone calls, in high security prisons have been validly used by priests in prisons to here confessions. This is equally a question of necessity, as state rules will not permit physical contact of inmates with anyone visiting them. Again the inmate is visually present, even though thick glass and/or bars that separate the two.
In the article, The Monk and the Murderer Fr. Kirk Larkin heard the confession of James Malicoat on the day he was executed at Oklahoma’s States Penitentiary infamous H-Unit on August 31st, 2005.
But at 10:45 a.m., under their own tension, the monk and the priest were ushered in to see Malicoat. After days of trying to conjure up what the killer would look like, Father Larkin was relieved to see a human being on the other side of the glass. Brother Vianney-Marie had never seen him look worse. Malicoat was slumped over for terror and want of sleep. "It's inhuman," the monk said. He was given about an hour with his last visitors, and Brother Vianney-Marie wasted no time. He made quick inquiries about Malicoat and his family and then introduced him to Father Larkin, telling Malicoat that he could make an act of faith and confess to him. He gave Father Larkin the telephone.
Malicoat told the priest he didn't want to confess.
"James was truly concerned about other people more than himself at this point," Father Larkin recalled. "He told me, 'Father, I don't want to burden you with the horrible things that I've done and that have been done to me over the course of my life.'"
The priest, with nothing rehearsed, trying to pry open the window that Brother Vianney-Marie had cracked, turned to the Profession of Faith. He went through the Creed point by point, asking Malicoat whether he agreed with each article.
Brother Vianney-Marie, his active participation relinquished, could hear only the priest's side of the conversation. He was in agony. When Father Larkin turned to apostolic succession and how a priest could forgive sin, the monk imagined how much time the explanation could eat up and couldn't take it any longer. He got up and went to the back of the room, where he paced and prayed the rosary out of earshot.
Brother Vianney-Marie looked up from his prayers in H-unit to see Father Larkin raising his hand in blessing over James Malicoat. The monk had no way of knowing whether this was absolution. But he could be pretty sure.
"I just knew it was his confession," Brother Vianney-Marie said. "I was ready to jump through the ceiling."
A few minutes later and Father Larkin was beckoning Brother Vianney-Marie back to Malicoat. Their half an hour apart had closed a chasm. And opened the window.
"All of a sudden, he had this weight off his conscience," Brother Vianney-Marie said. "I told him, 'I don't think you're my friend, you're my brother.' He has all the same graces. I said, 'Are you ready to go?' and he said, 'Yeah.' There was a peaceful tranquillity. He realized what he had done and was man enough to accept the consequences."
In the 23rd photo of the Tour of the Oklahoma State Penitentiary in McAlester - Photo Gallery one can see the location where Fr. Kirk Larson brought James Malicoat into the Church and heard his confession.
Fr. Larkin had maintained visual contact with James the entire time.
Further information may be gleaned from the following article: