My post on audio recordings in Garda custody is about establishing the grounds for the making of adverse inferences at trial, not about the procedure for interrogation in Garda custody.
Under Section 19A of the Criminal Justice Act 1984 (as inserted by Section 30 of the Criminal Justice Act 2007), it is open to a court to make an adverse inference (of guilt; what else?) arising from …the failure of an accused to mention… [“…any fact relied on in his or her defence in those proceedings, being a fact which in the circumstances existing at the time clearly called for an explanation from him or her when so questioned, charged or informed, as the case may be…]
Consider what this implies; it implies that, after the interrogation is over, the Gardai encounter the articulated defence of the accused and feel (presumably) that it is not credible, given the failure of the accused to refer to that defence during the interrogation. They can only ask the court to effectively, take the same view, if the conditions set out in Section 19A of the Criminal Justice Act 1984 (as inserted) are met. One of those conditions is that the interrogation is recorded electronically, or, with the permission in writing of the accused, recorded other than electronically.
Hence, to lay the ground for asking the court to make the adverse inference the Gardai must get the consent in writing of the suspect/accused to non-electronic recording where that form of recording is not available, or is not being used.